1 Appendix 1 Soil Contamination with Arsenic Reflects Groundwater

Appendix 1 Soil Contamination with Arsenic Reflects Groundwater Irrigation in Kandal Province, Cambodia Thomas Murphy1, Kongkea Phan2, Laurie Chan3, Alex Poulain3, Kim Neil Irvine4, David RS Lean5, Borey Ty7 1 Phnom Penh, 2International University, Phnom Penh, Cambodia; 3University of Ottawa, Canada; 4Nanyang Technological University, Singapore; 5Lean Environmental, Apsley, Ontario, Canada; 6Institute of Technology, Cambodia Edited and reposted June 2, 2018

In: Laurie Chan, Thomas Murphy, Alexander Poulain, Brian Laird, Kim Neil Irvine, David Lean, Kongkea Phan. 2017. Innovative solutions for food security/safety issues caused by arsenic contamination of rice in Cambodia. Final Technical Report. IDRC Project No: 107718-00020799032 Abstract The highest total arsenic measured in soil was 95 mg/kg. The concentration of arsenic in the rice paddy soils was highly variable and was generally higher near the irrigation wells. We demonstrated that even in the areas where groundwater irrigation was most commonly practiced with water rich in arsenic (Preak Russey), the use of rainwater water stored in ditches has the potential to alleviate the problem of elevated arsenic. We discovered a treatment ditch system that can remove > 95% arsenic from groundwater prior to irrigation. The rice produced by this system had equivalent concentrations of arsenic as rice grown in the same location, but only with surface water. Interviews of farmers and analysis of drinking water wells indicated that in the less contaminated areas of the arsenic zone, farmers are still using wells with arsenic concentrations higher than 50 µg/L. Introduction There are over 2.4 million people living in the arsenic contaminated zone of Cambodia (UNICEF 2009). Over 100,000 people are at high risk of chronic arsenic exposure (Sampson et al. 2008). Documented effects can be as subtle as impairment of intellectual development in children (Vibol et al. 2015), or extreme including amputations of limbs to remove cancerous growth (Gollogly et al. 2015). Congenital birth defects and mortality from arsenic are also well known. The most obvious source of arsenic toxicity is from drinking groundwater rich in arsenic. In some of the most contaminated sites, safe drinking water is now being provided. However, secondary sources of arsenic, such as arsenic that has been bioaccumulated into crops is also a concern. In Bangladesh, Banerjee et al. (2013) documented that in areas with good drinking water eating rice with more than 200 µg/L of arsenic is associated with significantly higher levels of cancer. Some rice in our research site has twice this threshold for cancer induction (Phan et al. 2013). Some rice in India and Bangladesh contains five times this threshold for cancer induction (Adomako et al. 2009). Irrigation with groundwater has taken place for more than twice as long in Bangladesh as Cambodia. The high concentration of inorganic arsenic in S and SE Asian rice has been called "a health emergency" (Brammer and Ravenscroft 2009). New EU guidelines for arsenic in rice products have resulted in half of such products exceeding guidelines (Baker 2014, Meharg 2014). Similar guidelines are proposed for USA, including arsenic in children's food of 100 µg/kg (US FDA 2016). One senior scientist has proposed that for children, the guideline for arsenic in food should only be 50 µg/kg (Meharg 2014). "China has the strictest regulations for 1

arsenic in rice at 150 μg Asinorganic kg-1, but, since rice is such a staple food in Asia, rice consumption remains a higher source of exposure than drinking water" (Sauve 2014). There are at least two reports of shipments of rice with arsenic being blocked (De Mel. 2011, Government India 2014), but there are more anecdotal stories (i.e., Rice News 2012). Future rice shipments will be blocked because of arsenic. There is an urgent need to improve the cultivation of rice to avoid Cambodian rice developing into the situation in Bangladesh, India and other countries. Farmers in our main research site are concerned about their health and rarely eat rice that they grow with groundwater. However, some farmers became very concerned that our research would interfere with their ability to sell rice. In a review of this concern the Commune Council allowed us to proceed mainly because of the applied component of our research work in full-scale treatments. The project adapted to the situation by using the special analytical equipment of the University of Ottawa to evaluate the critical variables influencing arsenic contamination in Cambodia, especially irrigation with groundwater. The advanced analytical capacity of the University of Ottawa does not exist in Cambodia. Methodology A map of the study area can be found in Figure 1. The control area, Kandal was along the flood plains of the Mekong River. Kandal could be reached via Highway 1 which is quite good. The Preak Russey sites were severely contaminated with arsenic, physically more concentrated and were located on the flood plains of the Tonle Bassac River. Road access to Preak Russey was via Highway 21B, a secondary road that took >2 hours each way, in good traffic and weather. Water sample collection Water samples were mainly collected from wells used to irrigate rice. Polyethylene bottles were filled to the top to exclude air. Sample collection was more awkward than first expected. Farmers irrigated as infrequently as once a week. Most of the farmers did not consistently use their phones and a smaller proportion did not use a phone. None of the farmers used the Internet. Some pumps were too difficult for older men or women to start. In Preak Russey, the deputy village chief or a more senior administrator in the Regional Commune Council helped make appointments for farmers and encouraged their support. Once the need for irrigation was finished for the season the pumps were removed from the fields and with that situation only three farmers agreed to take a water pump to the well so we could collect a well sample. We had no flow meters to test the flow rate of the pumps. Instead we used the specified flow rate as supplied by the manufacturer with an efficiency correction of x 0.7 for 30 m deep wells. Three pumps clearly were pumping at less than optimal conditions and these pumps were not included in our hydraulic analysis. Several well samples were collected in villages. Farmers rarely have fields adjacent to their houses; most lived in villages usually one to three kilometres away. Water samples were acidified quickly with 1 ml of concentrated nitric acid. In a small subset of duplicate water samples nitric acid was added in the field occasionally with a delay of an hour. The reason for this is that it is often very dangerous to use nitric acid in the field. There was a subset of this experiment in which water samples were not immediately acidified, were shaken with air to ensure oxidation, then let settle for 8 and 16 h prior to decanting and acidification. An additional treatment was conducted whereby the 16 h sample from above oxidation experiment was filtered with Whatman GFF filters prior to acidification. Water Sample Analysis

2

A total of 61 water samples were collected. All samples were shipped to Canada for analysis using ICP-MS. Trace elements in the water samples including arsenic were measured by Inductively Coupled Plamsa – Mass Spectrometry according to the US EPA Method 200.8 (US EPA 1994). Arsenic species including As (III), As (V), MMA, DMA were quantified using the method developed by Agilent Technologies (Agilent Technologies 2009). To compare the analytical capacity locally, thirty-one duplicated water samples were processed at the Institute of Technology for Cambodia on a Shimadzu AA-7000 using hydride generation for total dissolved arsenic and similarly nine samples were processed for total dissolved iron. All samples were filtered with 0.2 µm membrane syringe filters prior to dilution and analysis. Unless stated otherwise, all water data presented in this report is from the University of Ottawa.

Figure 1. Map of the Two Main Study Sites (shown by black arrows)

Soil Analysis Twenty-four soil samples were collected from Kandal. Fifty soil samples were collected from Preak Russey. A small Cambodian digging tool was used to extract soil plugs 10 cm long and about 4 cm wide. Typically for bulk integrated samples each field had three sites collected (>30 m apart) and at each sampling site triplicate samples (2 m apart) were collected to be combined, i.e. 9 scoops were combined in each field. For PR1, PR5, Kd3, and Kd9 a set of nine 3

such sites (each in triplicate scoops) were collected in a grid. Less intensive spatial distribution assessments were conducted in PR2, PR4, and PR9. The decision on the intensity a sampling was compromised by the availability of space to dry samples and the lack of insight into the site. Soil samples were air dried in an apartment and then ground with a mortar and pestle on a balcony. A set of 10 soil samples were freeze-dried at the University of Health Sciences to confirm that the soils were dry. Samples were sieved through a 100 µm mesh. Soil samples were typically more than 300 g. XRF Analysis of Soils Arsenic in soil was measured with a Niton XL3tGOLDD+ XRF handheld analyzer locally in Cambodia. The certified reference materials supplied by Thermo Fisher Scientific were used in each set of samples and arsenic was always within 5% of specifications. The counting time was usually one or two minutes but at times was increased up to 10 minutes. Longer counting was used when arsenic was less than 20 µg/g and to ensure a reading above non detect. All samples were processed using the sample cup method recommended by Thermo Fisher Scientific (2010, page 71). The sample cups (Double Open Ended: Cup/Ring/Cap, Suitable for Niton) came from (https://www.premierlabsupply.com/Products_for_LiquidsPowders/LiquidsPowders/Sample_Cu ps/id-SC-4331/Double_Open_Ended_CupRingCap_Suitable_for_Niton). The cups had an inside diameter of 2.4 cm, were 2.3 cm deep and held about 12.7 g of soil. The cups were sealed with Mylar film (Figure 2).

Figure 2. XRF Sample Cups Top is soil, bottom is a fertilizer.

Figure 3. Interview with farmer Mrs. Kim Leakina left, Dr. Murphy middle

Surveys of Farming Practices

4

As noted in the core report, the survey of farming practices was conducted in a series of phases. The Phase II survey which was the most refined, was conducted in 12 farms in Kandal Province along Highway 1 and in 18 farms in Preak Russey between February and September, 2016. The surveys were done in Khmer and translated into English by Mrs. Leakina Kim with Dr. Tom Murphy (Figures 3), and at various times with the additional assistance of Dr. Kim Irvine, Dr. Kongkea Phan, and Dr. Borey Ty. The survey is available after the references in Appendix 2. Site Details - Chance Discovery of a Treatment for Irrigation Water About one fourth of the farmers in the Preak Russey area used drainage ditches to remove excess water at the end of the rainy season. By chance, we discovered a farmer that was pumping water from his well, first into a ditch and then later on to his rice field (PR4). The ditch was 200 m long with a side channel. Our sampling was about 180 m from the pump. Also, by chance we discovered a farmer that first pumped water from a well into a ditch prior to irrigating his rice paddy (PR1) that was about 80 m away. Later at third farmer (PR10) used our insights and adopted this strategy of pumping water from his well into a ditch prior to irrigation of his fields. His ditch was >500 m long but only the first 100 m was sampled. These ditches were about 4 m wide and up to 2 meters deep. No chemicals were added to the irrigation water. No aeration was used. The only physical action was the introduction of nets to impede fish from entering the water pumps, but the nets also acted as a physical surface for periphyton growth and establishment of a layer of floating aquatic plants (i.e. hyacinth (Eichhornia crassipes). The floating plants impeded transport of floating scum to the pumps. Furthermore, no efforts were made to remove brush from the ditches which also acted as substrate for periphyton growth and impeded transport of floating scum to the pumps. Water samples were collected, once from PR4, once from PR10 and once from a treatment pond. Sample collection was restricted by the timing of irrigation, weather and our awareness of the situation. Once the rains had begun, well water in the ditches was diluted to unknown amounts. Sampling was avoided if rain had occurred the week before a trip. When the rains became vigorous, irrigation stopped. The floating orange scum was collected and freeze dried at the Fisheries Administration Ministry of Agriculture, Forestry and Fisheries, Cambodia. Then metals were determined by XRF analysis using the Camcontrol XRF analyzer (Niton XL3tGOLDD+ XRF) and a certified reference standard from Fisher Thermo Scientific. Results Water In Preak Russey, the mean concentration of total arsenic in 21 field wells was 959±351 µg/L (Table 1). By comparison the standards for arsenic in irrigation water in Australia, Japan and Taiwan are 100 µg/L, 10 µg/L and 50 µg/L, respectively (National Health and Medical Research Council 2004, Matsuno 2010, Lin et al. 2008) We complied with requests from our partners who helped us in the field to analyze their well water in the villages. Three tube wells in the Preak Russey village wells had a mean 626± 403 µg/L As. One shallow well (7 m deep vs 30 m deep for most) that was dug by Dr. Mickey Sampson at PR15 had only 1 µg/L total arsenic. Dr. Sampson intentionally dug the well shallow to minimize arsenic. In Preak Russey, the villagers now have access to piped water which has 4 µg/L total arsenic. Villagers had to pay for the use of piped water, some reports say the poor did not use it, but others say most share their water. By comparison in 4 field wells in Kandal (Highway 1) the mean and standard deviation were 65 µg/L and 51 µg/L. In 8 village wells in Kandal the mean and standard deviation were 46 µg/L and 30

5

µg/L. In Kandal all wells exceeded the WHO guidelines from 2 to 12 times. Unlike in Preak Russey, in Kandal, people often drank their well water. Four of these wells would not comply with the Cambodian guideline of 50 µg/L arsenic (Table 1). There is a lot of iron in the field wells of both Preak Russey and Kandal (Table 2). The mean concentration of iron was 9565±6635 µg/L (n=20) and 3695±3366 µg/L (n=10) in Preak Russey and Kandal field wells, respectively (Table 2). Much of this variability in the iron content was real and could be confirmed in simple jar tests where water samples were let stand without acid treatment. The extent of precipitation of iron varied greatly. The sample handling was professional but bias would be greater for the iron results to be underestimated than with the arsenic results. There was sometimes a delay in acidification of the samples, which was unavoidable because of the necessity to walk across one log "bridges" and jump ditches; it was not safe to carry acid. Table 3 shows that without immediate acidification but with acidification done three hours later, arsenic results were relatively stable but iron was not. The iron precipitated faster than arsenic but this had minimal effect on the arsenic data or likely no effect on the interpretation of the iron results. The famous Resource Development Laboratory (RDI), Kean Svay, Cambodia often used post acidification for their arsenic analysis. This was done for safety. This simple experiment validates RDI's results that for arsenic, acidification with nitric acid might not always be necessary in the field, but could be conducted hours later in the safety of a laboratory. This is not true for iron. Because of the uncertainty we used nitric acid as soon as possible usually within an hour of sample collection and always with full bottles. Ditch Management Because in the rainy season the fields in Preak Russey are usually flooded, drainage ditches were built >20 years ago. Many but not all farms have a ditch near them. Before our sampling, at times, these ditches were used to transport river water for irrigation. From Feb. 2016 to May 2016 they were used to trap and store rainwater. The total arsenic content of the rainwater in the ditches was 24.0±24.7 µg/L (Table 1). The variability reflects differing dilution of seepage water from fields with rainfall. The importance of this process was not initially understood so only four samples were collected. The ditch water had only about 5% the arsenic of the well water so it was a major improvement over well water. Treatment Ditches The treatment ditches were a subset of drainage ditches where well water was pumped into the ditches. After a residence time of >1.5 d in the ditch, the water was pumped >50 m from the well to irrigate the rice fields. At PR4, the first farmer with a treatment ditch, the irrigation well contained 1150 µg/L of arsenic and 20069 µg/L of iron. The treatment ditch was able to remove 99% of arsenic and 99% of iron prior to irrigation. The second farmer with a treatment ditch (PR10) had a well with 1044 µg/L of arsenic and 16742 µg/L of iron. At PR10, we confirmed that 94±3.8% (n=3) of the arsenic was removed. At PR 10 the arsenic removal occurred in the first 30 m but for iron the removal increased from 90% at both 30 m and 60 m from the well to 99%, 90 m from the well.

6

Table 1 Summary of Water Arsenic Analysis Kandal Field Wells Farm AsB As(III) DMA MMA As(V) ITC TotalAsUO Comment Code µg/L µg/L µg/L µg/L µg/L µg/L µg/L Kd1 nd 141.5 nd nd 307.0 448 1st field Kd1 nd 326.6 nd nd 276.2 603 2nd field Kd2 nd 39.7 nd nd 144.9 185 Field Kd3 nd 1.1 nd nd 70.7 27 72 Field Kd7 nd nd nd nd 10.5 27 10 Field Kd8 nd 2.4 8.5 nd 69.3 19 72 Field Kd9 nd nd nd nd 0.4 22 0 1st field Kd9 nd nd nd nd 0.1 65 0 2nd field Kd9 nd 0.0 0.0 nd 0.5 34 1 3rd field Kd10 0.14 59.8 nd nd 27.8 88 Fisheries nd 78.7 nd nd 26.4 34 105 Field blank1 nd nd nd nd 0.6 1 blank2 nd nd nd nd nd nd blank3 nd 0.0 0.0 nd 0.1 0 ITC Institute of Cambodia total arsenic TotalAsUO total arsenic University of Ottawa

Easting

Northing

105° 13’ 22.08”

11° 24’ 38.88"

105° 07’ 46.92" 105° 07’ 38.2” 105° 07’ 17.3” 105° 07’ 30.2” 105° 07’ 30.2” 105° 11’ 21.8”

11° 28’ 42.65” 11° 28’ 38.2” 11° 27’ 58.6” 11° 28’ 11.5” 11° 28’ 11.5” 11° 26’ 03.3”

Kandal Village Wells Kd2 nd 0.1 nd nd 46.5 47 Kd3 nd 0.1 0.1 nd 0.5 23 1 Kd4 nd nd nd nd 7.5 51 8 Kd5 nd nd nd nd 8.5 9 Kd6 nd 0.3 1.1 nd 19.5 150 20 Fisheries nd 43.4 nd nd 28.9 17 72 Fisheries is the Aquaculture Research Station nd = non detect ASB = Arsenobetaine

Village 105°11' 31.62" Village 105° 11’ 9.0" Village 105° 09’ 09.4” Village Village 105° 09’ 45.8” Village As(III) = arsenite

11°25' 56.07" 11°. 26' 00.2" 11° 27’ 39.8” 11° 27’ 19.4"

DMA = dimethylyarsinic acid MMA = monomethylarsonic acid

7

Table 1 continued Preak Russey Field Wells Farm Code PR1 PR1 PR2

AsB µg/L nd nd nd

As(III) µg/L 1163.8 57.4 625.8

DMA µg/L nd nd nd

MMA µg/L nd nd nd

As(V) ITC TotalAsUO µg/L µg/L µg/L 297.5 1658 1461 107.8 1502 165 410.7 1037

PR2Chy

nd

655.0

nd

nd

217.6

PR4 PR4adj PR6

nd nd nd

66.5 43.2 989.7

nd nd nd

nd 0.1 nd

566.7 706.9 170.8

PR6

nd

872.5

nd

nd

242.4

PR7

nd

602.7

nd

nd

176.2

PR8 PR8 PR9a

nd nd nd

264.7 237.6 994.1

nd nd nd

nd nd nd

272.8 178.9 275.8

PR9b

nd

359.4

nd

nd

474.8

PR9c

nd

794.7

nd

nd

289.9

PR10

nd

581.7

nd

nd

PR10b

nd

474.7

nd

PR12

nd

920.2

PR13

nd

PR14

Comment

Easting

Northing

Adjacent Field Field

105° 06’ 5.36" 105° 06' 01.96" 105o 06' 07.016"

11° 07’ 3.10” 11° 06’ 59.17” 11o 06' 56.109"

105o 06' 07.016"

11o 06' 56.109"

1147 1254

633 Field 105° 05'25.97" 750 Adjacent 105° 05'25.97" 1161 5/6/17 105o 06' 04.183"

11° 06'56.80" 11° 06'56.80" 11o 06' 57.624"

1409

1115

2/28/17 105o 06' 04.183"

11o 06' 57.624"

873 Field

105o 06' 04.92

11o 07' 06.60"

538 Field* 417 Field* 1270 Field1

105°.05’28.3” 105°.05’28.3” 105o 06' 03.671"

11°08 10.2” 11°08 10.2” 11o 06' 48.605"

834 Field1

105o 06' 01.294"

11o 06' 48.879"

1085 Field3

105o 06' 06.869"

11o 06' 47.280"

462.4

1044 Field1

105o 05' 17.01"

11o 06' 56.63"

nd

476.3

951 Field2

105o 05' 19.719"

11o 06' 53.127"

nd

nd

327.3

1248 Field

105o 06' 31.514"

11o 07' 19.94"

582.7

nd

nd

304.7

887 Field

105o 06' 33.206"

11o 07' 15.488"

nd

518.3

nd

nd

451.4

970 Field

105o 06' 34.822"

11o 07' 13.864

PR16

nd

757.0

nd

nd

464.2

1221 Field

105o 05' 58.136"

11o 07' 11.919"

PR19

0.01

1504.1

nd

nd

201.6

1706

779 Field 898

898

Field_adj is the field immediately to the east of PR1, no interview *PR8 was sampled twice; the well had gone dry and was dug deeper Adjacent is east of PR4, no interview

PR6 was sampled twice

8

Table 1 continued Preak Russey Village Wells AsB As(III) DMA MMA As(V) Farm µg/L µg/L µg/L µg/L µg/L Code PR2 PR7 **

nd nd nd

765.0 396.3 72.4

nd nd nd

nd nd nd

216.2 312.7 116.3

PR15 In Pipe

0.0

0.1

nd

nd

1.2

0.0

0.3

**No interview,

ITC µg/L

TotalAsUO µg/L 981 709 189

Comment

Easting

Northing

Village Village **

105° 06’ 03.62” 105° 05’ 47.8" 105o 05' 53.99"

11° 07’ 30.83” 11°07’ 52.8” 11o 07' 43.37"

105o 06' 43.78"

11o 07' 30.17"

1 5 m deep 4

3.6

Most wells were 30 m tube wells but PR15 was only 5 m and was hand dug,

Preak Russey Treatment Ditches -with well source shown again. PR4 nd 66.5 nd nd 566.7 1147 PR4 0.2 1.3 0.5 0.1 2.9 157 PR10 nd 581.7 nd nd 462.4 PR10 1.0 15.4 8.6 0.9 22.9 PR10 0.7 6.2 7.1 1.3 30.5 PR10 0.6 78.0 6.2 1.0 29.3 No rain had occurred for weeks before these samplings. Preak Russey Drainage Ditches PR2 1.5 3.1 8.4 PR4 0.8 1.8 0.2 PR4 1.3 0.8 0.1 PR15 0.4 2.0 0.2

1.1

At PR2 there had been no rainfall for weeks. In 2017, the PR4 ditch trapped rainwater.

56.9 13.5 4.5 17.8

217 174 257

633 Well 4 Treated

In pipe was treated water

105° 05'25.97" 105° 05'25.97"

1044 Well 105° 05' 17.01" 38 Treated 105° 05' 17.01" 37 Treated 105° 05' 17.01" 107 Treated 105° 05' 17.01" In 2016, PR was a treatment ditch.

60 16 7 20

Seepage Main Side Main

105° 06' 07.02" 105° 05'25.97" 105° 05'25.97" 105° 06' 43.78"

11° 06'56.80" 11° 06'56.80" 11° 06' 56.63" 11° 06' 56.63" 11° 06' 56.63" 11° 06' 56.63"

11° 06' 56.11" 11° 06'56.80" 11° 06'56.80" 11° 07' 30.17"

The other 3 samples were diluted by rain.

9

Table 1 continued Treatment Pond Farm AsB As(III) DMA MMA As(V) TotalAsUO Easting Code µg/L µg/L µg/L µg/L µg/L Inlet 0.0 1504.1 nd nd 201.6 1706 105° 06' 12.77" Outlet 0.0 63.8 nd nd 1335.0 1399 105° 06' 12.77" 100 m 0.6 2.4 1.3 0.3 828.9 834

Northing 11° 07' 21.03" 11° 07' 21.03"

In spite of the pond only having a 5 minute retention time, 95% of arsenite was oxidized. Some arsenic removal (18%) may be real. Pond needed more emergent plants and debris for surface reactions, including periphyton. Pond needed longer retention time. >100 m is a sample of the main flow 100 from the pond. The freeze-dried floating orange scum collected in PR10 contained 125±8 µg/g or ppm of arsenic and 24946±202 µg/g of iron. The iron content likely accounts for the orange colour of the floc, but the precipitation might be more complicated than a direct chemical reaction of iron with arsenic. The floc floated because of a high content of gas presumably reflecting microbial biooxidation (Stolz et al. 2006. Osborne et al. 2010). In a simple experiment with well water, iron, but not arsenic readily precipitated (Table 3). Further sampling is of course warranted, the mechanism of precipitation is not clear, but initial observation indicate strongly that it is important to restrict movement of the floating scum to the pumps that irrigate the fields. The floating scum was also observed in the rice fields that were directly irrigated with well water. When the rice was young, the floating scum/bio-oxidation floc could be readily blown by the wind. This could clearly impact on the distribution of arsenic in soils. In theory, a small proportion of the rice fields could be used to trap arsenic but the long-term management of that site would need assessment. Ferns have been shown to be affected at arsenic removal from water (Danh et al. 2014), but such plants would be potentially toxic to animals such as cattle that frequently are around the rice fields. Moreover, disposal of the toxic ferns would consume energy, time and land. Alternate options/crops for such a trap might exist. PR4 believed that with his style of irrigation his rice grew taller and was more productive. At 7/tonnes per hectare, PR4 was the 2nd most productive rice farmer of 25 farms reporting their productivity. Certainly, his rice was among the healthiest looking rice. Another nearby farmer (PR17) claimed that when he was unable to dilute the groundwater with surface water, his rice productivity was reduced and his cucumbers were stunted. But the only scientific analysis is a comparison of the effects of arsenic on rice production in Bangladesh. In a controlled experiment in India irrigation with 1000 µg/L of arsenic suppressed rice production by 52% (Azad et al. 2012).

10

Table 2 Kandal Field Wells Farm Code Kd1 Kd1 Kd2 Kd3 Kd7 Kd8 Kd9 Kd9 Kd9 Kd10 Fisheries Blank

Al 524 15 82 332 129 6 216 452 240 10 132 287

Cr 1.2 0.2 0.3 0.6 0.4 0.1 0.4 0.9 0.4 0.1 0.3 0.6

Mn 195 239 148 327 2058 327 601 626 511 617 1942 182

Fe 8746 6273 2867 3779 636 8590 277 506 216 5057 191 220

Ni 1.3 0.0 0.3 0.7 0.8 0.5 0.5 0.7 1.0 0.1 0.3 0.7

Cu 2.0 0.3 0.4 1.1 1.0 0.2 1.3 1.0 1.0 0.3 0.5 1.3

Zn 12.6 3.6 3.3 1.9 4.5 0.8 7.8 9.7 5.3 14.5 1.6 4.8

Ba 730.4 376.5 281.6 241.1 84.3 127.3 113.4 115.6 40.9 236.1 18.2 37.3

Pb 0.7 0.0 0.1 0.9 0.4 0.1 1.0 1.0 4.0 0.1 0.2 12.4

Mg 23564 14378 12131 11498 16455 15704 31738 32571 17858 13224 20991 17043

Easting

Northing

105° 13’ 22.08”

11° 24’ 38.88"

105° 13’ 22.08” 105°11' 31.62" 105° 11’ 9.0" 105° 07’ 46.92" 105° 07’ 38.2” 105° 07’ 17.3” 105° 07’ 30.2” 105° 07’ 30.2” 105° 11’ 21.8”

11° 24’ 38.88" 11°25' 56.07" 11°. 26' 00.2" 11° 28’ 42.65” 11° 28’ 38.2” 11° 27’ 58.6” 11° 28’ 11.5” 11° 28’ 11.5” 11° 26’ 03.3”

0.3 0.4 0.5 1.8 0.4 0.4 121.7

5.2 51.2 5.8 16.3 2.9 5.2 304.0

175.8 43.8 265.6 255.5 621.5 326.7 27.2

0.7 0.1 2.3 86.1 0.2 0.1 0.5

24540 24596 16230 17134 24472 14094 41745

105°11' 31.62" 105° 11’ 9.0" 105° 09’ 09.4”

11°25' 56.07" 11°. 26' 00.2" 11° 27’ 39.8”

105° 09’ 45.8”

11° 27’ 19.4"

Kandal Village Wells Kd2 20 0.3 1880 12557 0.0 Kd3 13 0.1 2075 48 0.2 Kd4 11 0.0 209 2249 0.0 Kd5 103 0.1 222 1895 0.1 Kd6 9 0.0 1124 2103 0.5 Kd10 15 1.0 374 3584 0.1 Fisheries 12 56.7 2727 33632 24.1 Fisheries is the Aquaculture Research Station

all values = µg/L

11

Table 2 continued Preak Russey Field Wells Al Cr Mn 40 0.2 509 6 0.2 175 15 0.2 529

Fe 2913 17559 4615

Ni 0.3 0.3 0.4

Cu 1.4 0.8 0.7

Zn 5.8 0.2 1.8

Ba 13 43 1195

Pb 0.5 0.0 0.1

Mg 26777 12269 19928

Easting

Northing

105° 06’ 5.36" 105° 06' 01.96"

11° 07’ 3.10” 11° 06’ 59.17”

105o 06' 07.016"

11o 06' 56.109"

PR2-Chy PR4 PR4adj5 PR6

7

3798

0.5

0.4

3.3

977

0.1

13367

105o 06' 07.016"

11o 06' 56.109"

9 0.2 157 31 0.2 219 14 0.1 590

20069 23677 3812

1.5 1.7 0.3

0.2 0.4 0.6

3.8 3.4 0.9

1781 2695 961

0.0 0.0 0.1

42125 53611 17546

105° 05'25.97" 105° 05'25.97"

11° 06'56.80" 11° 06'56.80"

105o 06' 04.183"

11o 06' 57.624"

PR6

27 0.2 579

3705

0.3

0.8

3.1

15

0.0

17755

105o 06' 04.183"

11o 06' 57.624"

PR7 PR8 PR8 PR9a

22 0.2 590

3355

0.2

0.8

0.3

928

0.1

26382

105o 06' 04.92

11o 07' 06.60"

73 0.3 759 80 0.3 777 23 0.2 649

13491 12450 3607

0.3 0.3 0.6

0.4 0.7 1.8

2.0 15.7 7.2

1023 1149 970

0.2 0.1 0.1

33580 40110 16823

105°.05’28.3” 105°.05’28.3”

11°08 10.2” 11°08 10.2”

105o 06' 03.671"

11o 06' 48.605"

PR9b

28 0.3 620

3958

1.0

2.0

10.7

883

0.1

14778

105o 06' 01.294"

11o 06' 48.879"

PR9c

33 0.2 354

4604

0.7

0.7

7.9

698

0.1

9910

105o 06' 06.869"

11o 06' 47.280"

PR10

22 0.3 208

16742

0.8

0.5

2.6

1965

0.0

50523

105o 05' 17.01"

11o 06' 56.63"

PR10b

32 0.3 228

16645

1.3

0.6

0.7

1732

0.1

44306

105o 05' 19.719"

11o 06' 53.127"

PR12

16 0.1 984

6423

0.4

0.4

0.8

1936

0.0

34749

105o 06' 31.514"

11o 07' 19.94"

PR13

10 0.3 1341

11885

0.5

0.6

1.0

2210

0.1

33973

105o 06' 33.206"

11o 07' 15.488"

PR14

6

12321

0.7

0.2

tonne per hectare per year. To excavate, grind and ship this amount of laterite from a deposit in Mondulkurri (mountainous area of Cambodia) cannot likely be done within the budget of a rice farmer. There are strong reasons to be concerned about toxicity of high iron applications, including the current irrigation with groundwater and suggested remedial options with iron. High levels of iron in soil both block nutrient assimilation (Lacoma 2017) and produce oxidative stress in plants (Kampfenkel et al. 1995). Iron toxicity has been identified in rice paddies in India, Indonesia, Malaysia and Philippines (Tanaka and Yoshida 1970, Mitra et al. 2009, Buresh and Quilty 2017). Rice fields are prone to iron toxicity because of the anoxia resulting from long periods of flooding that dissolves iron. Relative to the extensive publications on arsenic toxicity, iron toxicity does not get much attention. Of course, iron toxicity mainly affects rice productivity and relatively is not much of a toxic concern to people. Whereas, the primary health concern remains arsenic. One of the reasons that CEDAC (2016, Cambodian NGO) discourages use of groundwater for irrigation is that it forms yellow soils of low productivity. Any irrigation technique that results in extensive periods of standing water and anoxia will produce iron toxicity (Buresh and Quilty 2017). The SRI approach that CEDAC encourages would decrease iron toxicity significantly because this technique does not flood soils for extensive periods which results in low oxygen and high iron solubility. Iron toxicity might influence other general aspects of agriculture in our study area. Corn or beans were never found growing on soil with more than 20 µg/g of arsenic but the relationship might reflect the common belief of farmers that these soils were too poor for corn or beans. Two farmers (PR4, PR17) claimed that undiluted groundwater suppressed their rice production and

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PR17 claimed that undiluted groundwater stunted his cucumbers. Arsenic might be a problem limiting the growth of more sensitive plants than rice but the potential for other variables like iron toxicity from groundwater mediating this relationship is high. Note that the iron content of the groundwater in Kandal was only half that of Preak Russey. Corn and beans were more commonly grown in Kandal than in Preak Russey. In India, iron toxicity is treated by addition of lime or potassium (Mitra et al. 2009). Usually, potassium is not considered as important as phosphorus and nitrogen in rice but it is more likely to be important in iron rich soils, especially for farmers only using diammonium phosphate. Relative to the effort we put into evaluating phosphorus limitations in NPK fertilizers, we did much less with potassium. But, there also seems to be a deficiency of potassium in half of the NPK fertilizers (Figure 7, Appendix 3). The Rice Institute reviews treatment options but states that there is "no practical field management option to treat iron toxicity" (Buresh and Quilty 2017). If possible, it is best avoided. Although there has been some limited amount of work done on the differences between gross and net accumulation of arsenic from groundwater irrigation (Dittmar et al. 2007), there does not seem to be as rigorous analysis on iron loading and erosion rates to and from rice paddies. Perhaps it could be done using XRF analysis of soils but it would be a lot of work and years to get good statistical results. Moreover, care has to be taken with the selection of control sites. There does not seem to be a significant correlation between total iron and total arsenic in fields where the arsenic changes dramatically around the irrigation well. More soil analysis could help interpret the buildup of iron and its potential toxicity in soil. Groundwater analysis might also assist in interpretation of iron toxicity and iron's effect on arsenic. The field at Preak Russey with the highest concentration of iron in soil has never received groundwater irrigation (PR15-"river" field). Water flow shows that PR15 has the lowest elevation but there does not seem to be any detailed analysis of elevation. There are variations in elevation of a few meters, perhaps five meters. Many of the farmers believe that there is an old river course that PR15 is on. Iron is known to seep in groundwater and accumulate as "bog iron" in soils at lower elevations. There are some farms in Preak Russey that only have used irrigation with surface water (good controls) and other farms in Preak Russey have used groundwater irrigation for up to 20 years. As long as the water column above the soil remains somewhat oxic, iron will not be as mobile as arsenic. Furthermore, arsenic has some capacity for volatilization as trimethyl arsine which iron does not. How quickly, soils will become toxic from excess iron loading is not clear and farm management would have a great impact on the geochemistry including iron toxicity, arsenic solubility and phosphorus availability. Analysis of the most toxic forms of iron and variables that effect it would require analysis of the soil pore water with diffusion chambers. The types of fertilizers will affect pH but the effects vary and can be short lived. Adding organic matter such as straw or manure to fields would reduce oxygen and increase iron toxicity. Although the original proposed intervention method, SRI does not seem to be feasible in Preak Russey, there are alternative and similar concepts to consider. One of the PIs (Tom Murphy) of this project had worked for many years in several areas in Japan where rice is grown. Most farmers utilize drawdown of the water table in mid-crop which oxidizes the soil. Farmers in Japan have one very common feature with Cambodian farmers; they are old and would not tolerate a practice that required more extensive weeding. Mid-season drawdown is one of the strategies suggested by the International Rice Institute to minimize iron toxicity (Buresh and Quilty 2017). There are other equivalent methods, at least in terms of the objective of using less water, producing

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oxic soils, increasing phosphorus availability, and increasing rice productivity. The Alternative Wet Dry (AWD) method warrants consideration (Howell et al. 2013). It also uses less water which is important as water supplies become more limiting and of course reduces both arsenic and iron toxicity. Ideally, the process would initially be monitored for basic geochemical analysis to confirm that the watering regime produced the desired conditions. The acid test would still be it’s ability to produce rice without considerably more effort weeding. It's not clear which geochemical variables could be monitored to accomplish the required conditions for good rice growth but not enhance weed growth. Is it possible to achieve both? The primary reason for developing surface water storage of water is to avoid arsenic toxicity. But for long-term productivity of soils, iron toxicity should be avoided as well and water storage in ditches and wetlands has to be considered and developed. Whatever irrigation approach is used has to consider the hesitation of farmers to flush extra water to produce oxic conditions. This is one of the reasons for the failure of the SRI approach in Cambodia (Ly et al. 2012). They need reliable water supplies. Plus, construction of and maintenance of irrigation canals is expensive. The largest farmer at Preak Russey spends about $50/ha per year maintaining his ditches. Figures 7 shows the reconstruction of a 2.8 km long ditch from the Bassac River to Preak Russey project site. Moreover, there were already concerns that within 15 years there will not be enough water in the Mekong River system to sustain irrigation in the dry season (Erban and Gorelick 2016). Figure 8 shows that there is a large wetland only a few km from the Preak Russey site that physically would be useful for a water storage site. Figure 9 illustrates the degree of flooding on a wet year; there is lots of water, but not in the dry season. Water storage is also required for aquaculture and should be coordinated with rice culture to synergize rice and fish production.

Figure 7 Rebuilt Irrigation Canal to Provide Water to Preak Russey The red arrows on the map point to the path of the 2.8 km irrigation canal to the farmers in this study, which are represented by yellow pins,

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Figure 8 Large Wetland Near Preak Russey Yellow pin on top is a wetland 2-3 km from rice fields The lower yellow pins are 3 of our farm sites

Figure 9 Wet Season Flooding Taken 4 km north of Phnom Penh from a commercial flight

Effect of Sulphur on Iron-Arsenic Reactions and Remediation Sulphur could be considered as a potential remediation method for iron toxicity and reduced arsenic assimilation as a research topic. Ravenscroft et al. (2009) state that sulphur is a common limiting nutrient in south-east Asian rice paddies. There are two site specific reasons for considering sulphur application to Prek Russey. 1) Fan et al. (2013) documented that sulphur can decrease arsenic bioaccumulation in brown rice in China. 2) Formation of iron sulphide would likely overcome iron toxicity. There is a third general justification to consider sulphur applications, at least in a research mode. Sulphur addition in wetlands or rice paddies will switch microbial processes to block methane release from rice paddies. In theory, but not now, reducing methane releases from paddy fields might someday qualify farmers to receive carbon credits (Murphy et al. 2013). There are at least two reasons to hesitate on large-scale treatments with sulphur. 1) Fan et al. (2013) state that the sulphur mediated enhanced precipitation of iron, reduced rice productivity and 2) was not completely effective in blocking arsenic assimilation. The latter observation is consistent with our observations at Preak Russey. Iron precipitation in the Preak Russey fields is already quite dramatic, apparently decreases arsenic assimilation, but the treatment is incomplete and the arsenic risks continue. It would be more effective to have the arsenic in irrigation water treated in a ditch prior to irrigation. Treatment ditches at Preak Russey removed 95% of the iron from the irrigation water prior to application to the fields. First, the treatment ditches have to be optimized, but the longterm management options have to be considered to guide applied research sampling. Some of the arsenic likely leaves the treatment ditch as trimethyl arsine (TMA), but the iron would persist in the ditch soils. Eventually the ditch would have to be redug to maintain its hydraulic capacity. Normally the soils excavated from the ditch are reapplied to the berms around the paddy fields. Already, some of the mud that is in the bottom of the treatment ditch is removed from the ditch as part of a collection of fish. Farmers push the mud slurry though a net and towards and into a larger ditch. In Figure 10 you can see two young farmers covered in mud taking a break while two older farmers harvest fish in the treatment ditch behind them. The mud covered pail was half full of small fish. The two women were collecting rice samples. The long-term sustainability of the treatment ditch concept is not clear but without doubt it is much preferable to the direct use of

26

groundwater. Nothing else appears to be as cost-effective as the treatment ditch. It should be optimized at least as a band aid until systems are built to store surface water for irrigation and probably aquaculture at the same time.

Figure 10 Rice Collection and Fishing in Treatment Ditch The two farmers in the ditch (right side) are removing fish from the mud remaining in the drained treatment ditch and inadvertently pushing the mud out of the treatment ditch into a larger drainage ditch. Recommendations Further evaluation of the effectiveness of a treatment ditch in removing arsenic is needed. Some aspects of the treatment ditch would best be evaluated in a controlled experiment on a farm that was rented for a three-year period. Aspects of the toxicity of the irrigated water compared to the treated water could only be done in such an experimental design. Likewise, the effects of the irrigated water on bioaccumulation in rice and soil would best be done with control over all aspects of the farming. The cost for land rental, technical direction and field help is minor compared to the potential significance of continuing to produce rice with arsenic. Long-term monitoring is required to assess any potential accumulation of arsenic in the ditch and mobilization of the arsenic into the fields. Irrigation Ditches Most farmers now understand that ditches improve their storage/access to surface water and that such water produces rice with less arsenic. This education and management must expand with more ditches. Furthermore, treatment ditches remove arsenic effectively but to optimize their use, the mechanism of arsenic removal must be understood. The likely mechanism of

27

volatilization of trimethyl arsine (TMA) gas could be evaluated with silver nitrate traps processed overseas such as in Canada. TMA gas trapping should be evaluated in treatment ditches, in rice paddies and in air near rice paddies. Likely TMA production is substantial in the rice paddies and that optimization of TMA production in treatment ditches does not change of volatilization of arsenic in the general area. Dilution of TMA is likely large but some assessment of ambient air near the rice paddies would help manage health concerns with appropriate risk assessment. Soil Analysis XRF is an effective tool for the XRF analysis of arsenic contamination in soils. We now have the insights to design more intensive soil sampling, to assess net versus gross arsenic loading to soils. Confirmation that net loading is substantially less than gross loading would help design improved arsenic management. For example, as long as most arsenic leaves the field by monsoon flushing or TMA production, the emphasis should be on treatment of the irrigation water, not inactivation of arsenic in soil.

References Adomako E, Solaiman ARM, Williams PN, Deacon C, Rahman GKMM, Meharg AA. 2009. Enhanced transfer of arsenic to grain for Bangladesh grown rice compared to US and EU Environ Int 35:476–479. Agilent Technologies 2009. As Speciation Analysis Handbook. Rev. A, Agilent Technologies, Inc. 9-1 Takakura-cho, Hachioji-shi, Tokyo 192-8510 Japan. Andres J, and PN Bertin. 2016. Microbial genetics of arsenic. FEMS Microbiology Reviews, Volume 40(2) 299–322. https://doi.org/10.1093/femsre/fuv050. Arsenic, 2009. Arsenic: Environmental Chemistry, Health Threats and Waste Treatment. 2009. ed. Kevin Henke. John Wiley & Sons, Science - 588 pages Azad MAK , Mondal AHMFK , Hossain MI, Moniruzzaman M. 2012. Effect of Arsenic Amended Irrigation Water on Growth and Yield of BR-11 Rice (Oryza sativa L.) Grown in Open Field Gangetic Soil Condition in Rajshahi. J. Environ. Sci. & Natural Resources, 5(1): 55-59, 2012 ISSN 1999-7361. Baker K. 2014. Cereal killers? More than half of rice products including Rice Krispies and Heinz baby rice exceed new EU limits for Arsenic. The Daily Mail. Available at: http://www.dailymail.co.uk/news/article-2817542/More-half-rice-products-exceed-new-EUlimits-ARSENIC.html#ixzz4GtpuRvi6 Banerjee M, Banerjee N, Bhattacharjee P, Mondal D, Lythgoe PR, Martınez M, Pan J, Polya DA, Giri AK. 2013. High arsenic in rice is associated with elevated genotoxic effects in humans. Scientific Reports 3: 2195 | DOI: 10.1038/srep02195. Available at: http://www.nature.com/articles/srep02195 Brammer H, Ravenscroft P. 2009. Arsenic in groundwater: A threat to sustainable agriculture in South and South-east Asia. Environ Int 35:647–654. Buresh R and J. Quilty. 2017. Iron (Fe) toxicity. Rice Knowledge Bank. International Rice Research Institute. http://www.knowledgebank.irri.org/training/fact-sheets/nutrientmanagement/deficiencies-and-toxicities-fact-sheet/item/iron-toxicity Burt CM, Orvis S; Alexander N. 2010. Canal seepage reduction by soil compaction. J. Irrig. Drain Eng. 135:479. Available at: http://www.itrc.org/papers/canalseepage.htm

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CEDAC. 2015. Tong C. Personal communication, Center for Study and Development in Agriculture, Phnom Penh, Cambodia. http://www.cedac.org.kh/ Danh, L. T., Truong, P., Mammucari, R. & Foster, N. A. 2014. Critical review of the arsenic uptake. Mechanisms and phytoremediation potential of Pteris vittata. Int. J. Phytorem. 16, 429–453 . De Mel, R. 2011. Arsenic in rice grossly exaggerated claims Croplife. Sri Lanka Rice. Available at http://www.ft.lk/article/38943/Arsenic-in-rice-grossly-exaggerated-claims-Croplife. Dittmar J, A. Voegelin, LC Roberts, SJ Hug, GC Saha, MA Ali, ABM Badruzzaman, and R Kretzschmar. 2007. Spatial Distribution and Temporal Variability of Arsenic in Irrigated Rice Fields in Bangladesh. 2. Paddy Soil. Environ. Sci. Technol 41 (17):5967–5972. Down S. 2009. Arsine trap for soil emissions. Ezine. John Wiley and Sons, Ltd. Available at: http://www.separationsnow.com/details/ezine/sepspec22534ezine/Arsine-trap-for-soilemissions.html?tzcheck=1,1,1,1,1&&tzcheck=1 Dutch Target and Intervention Values, 2000. The New Dutch List. Dutch Government. ANNEXES Circular on target values and intervention values for soil remediation. https://www.esdat.net/Environmental%20Standards/Dutch/annexS_I2000Dutch%20Environm ental%20Standards.pdf Erban LE, SM Gorelick. 2016. Closing the irrigation deficit in Cambodia: Implications for transboundary impacts on groundwater and Mekong River flow. J. Hydrology 535:85–92. Fan J, X Xia, Z Hu, N Ziadi, C Liu. 2013. Excessive sulfur supply reduces arsenic accumulation in brown rice. Plant Soil Environ. Vol. 59, 2013, No. 4: 169–174. Gollogly JG, Gascoigne AC, Holmes C, Kamp EM, Jenni K, Vath SB. 2010. Arsenic and amputations in Cambodia. Asian Biomed Vol (3): 469-474 Government of India. 2014. http://www.aau.in/sites/default/files/circular/pseti_basmati_rice_dro_june_14.pdf Howell KR, P Shrestha, IC Dodd, 2013. Alternate wetting and drying irrigation for rice in Bangladesh: Is it sustainable and has plant breeding something to offer? Food and Energy Security 2013; 2(2): 120–129 Huang H, Y Jia, G-X Sun, Y-G Zhu. 2012. Arsenic Speciation and Volatilization from Flooded Paddy Soils Amended with Different Organic Matters. Environ Sci Technol 46 (4), pp 2163– 2168. https://www.ncbi.nlm.nih.gov/pubmed/22295880 Jakob R, A Roth, K Haas, EM Krupp, A Raab, P Smichowski, D Gomez, J Feldmann. 2010. Atmospheric stability of arsines and the determination of their oxidative products in atmospheric aerosols (PM10): evidence of the widespread phenomena of biovolatilization of arsenic. J Environ Monitor 12(2):409-16. DOI: 10.1039/b915867g · Source: PubMed. Available at: https://www.researchgate.net/publication/41420268_Atmospheric_stability_of_arsines_and_t he_determination_of_their_oxidative_products_in_atmospheric_aerosols_PM10_evidence_of _the_widespread_phenomena_of_biovolatilization_of_arsenic Jia Y, H Huang, G-X Sun, F-J Zhao, Y-G Zhu. 2012. Pathways and Relative Contributions to Arsenic Volatilization from Rice Plants and Paddy Soil. Environ Sci Technol 46(15):8090-6. https://www.researchgate.net/publication/22805941 Kampfenkel K, M Van Montagu and D Inzé. 1995. Effects of Iron Excess on Nicotiana plumbagnifolia Plants, Implications to Oxidative Stress. Plant Physiol. 107: 725-735.

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Kruger MC, PN Bertin, HJ Heipieper, F Arsène-Ploetze. 2013. Bacterial metabolism of environmental arsenic - Mechanisms and biotechnological applications. Appl Microbiol Biotechnol (2013) 97:3827–3841 DOI 10.1007/s00253-013-4838-5. Lacoma T. 2017. The Effect of Excess Iron in Plants. https://sciencing.com/effect-excess-ironplants-5526745.html. Lee DY and Lee CH. 2001. Regulatory Standards of Heavy Metal Pollutants in Soil and Groundwater in Taiwan Regulatory Standards of Heavy Metal Pollutants in Soil and Groundwater in Taiwan. Available at: https://sgw.epa.gov.tw/ReSAG/Update_Data/Information8839253Nov30_01Regulatory%20S tandards%20of%20Heavy%20Metal%20Pollutants%20in%20Soil_20111116.pdf Lee, M., Paik, I.S., Do, W. et al. 2007. Soil washing of As-contaminated stream sediments in the vicinity of an abandoned mine in Korea. Environ Geochem Hlth, 29(4), 319–329. Lin HT, SW Chen, CJ Shen and C Chu. 2008. Arsenic species in groundwater in paddy fields with high soil arsenic. Proceedings of 14th International conference on heavy metals in the environment. Nov 16-23, 2008. Taipei, Taiwan. Available at: http://public.tactri.gov.tw/pdf/2008/arsenic%20species%20in%20groundwater.pdf Ly P, LS Jensen, TB Bruun, D Rutz, A de Neergaard. 2012. The System of Rice Intensification: Adapted practices, reported outcomes and their relevance in Cambodia. Agr Syst 113:16-27. Matsuno Y. 2010. Monitoring and Management of Irrigation Water Quality in Japan. Food and Fertilizer Technology Center Available at: http://www.fftc.agnet.org/library.php?func=view&id=20110726150303&type_id=4 Meharg A. 2014. High levels of arsenic in rice: why isn't it regulated in our food? The Conversation. Available at: http://theconversation.com/high-levels-of-cancer-causingarsenic-in-rice-so-why-isnt-it-regulated-in-our-food-33691 Mestrot A, MK Uroic, T Plantevin, Md R Islam, EM Krupp, J Feldman, AA Meharg. 2009. Quantitative and Qualitative Trapping of Arsines Deployed to Assess Loss of Volatile Arsenic from Paddy Soil. Environ Sci Technol 43(21):8270–8275. Available at: https://www.researchgate.net/publication/316047077_Quantitative_and_Qualitative_Trapping _of_Arsines_Deployed_to_Assess_Loss_of_Volatile_Arsenic_from_Paddy_Soil Mestrot A, J Feldmann, EM Krupp, MS Hossain, G Roman-Ross, AA Meharg. 2011a. Field Fluxes and Speciation of Arsines Emanating from Soils. Environ Sci Technol 45: 1798-1804. Available at: https://www.researchgate.net/publication/4980134 Mestrot,A., Feldmann, J., Krupp, E.M., Hossain, M. S., Roman-Ross, G., Meharg. A. A., 2011b. Field fluxes andspeciation of arsines emanating from soils. Environ. Sci. Technol. 45, 17981804. Available at:https://www.researchgate.net/publication/49801344_Field_Fluxes_and_Speciation_of_Arsi nes_Emanating_from_Soils Mestrot, A., Planer-Friedrich, B., Feldmann, J., 2013. Biovolatilization: a poorly studied pathway of the arsenicbiogeochemical cycle. Environ. Sci.: Processes and Impacts, doi: 10.1039/C3EM00105A. Available at:https://www.researchgate.net/publication/245028421_Biovolatilisation_A_poorly_studied_ pathway_of_the_arsenic_biogeochemical_cycle Ministry of Environment 1991. Government of Japan. http://www.env.go.jp/en/water/soil/sp.html. Mitra GN, SK Sahu and RK Nayat. 2009. Ameliorating effects of potassium on iron toxicity in soils of Orissa. Available at:

30

https://www.ipipotash.org/udocs/Amelioration_Effect_of_Potassium_on_Iron_Toxic_Soils_o f_Orissa.pdf Murphy, T.P., K. Irvine, and M. Sampson. 2013. The Stress of Climate Change on Water Management in Cambodia, With a Focus on Rice Production. Climate and Development. 5:(1)77-92 National Health and Medical Research Council (2004) Australian Drinking Water Guidelines 6 , Natural Resource Management Ministerial Council, Australian Government. Osborne TH, HE Jamieson, KA Hudson-Edwards, DK Nordstrom, SR Walker, SA Ward and JM Santini. Microbial oxidation of arsenite in a subarctic environment: diversity of arsenite oxidase genes and identification of a psychrotolerant arsenite oxidiser. BMC Microbiology201010:205. https://bmcmicrobiol.biomedcentral.com/articles/10.1186/14712180-10-205 Phan K, Sthiannopkao S, Heng S, Phan S, Laingshun Huoy L, Wong MH, Kim K-W. 2013. Arsenic contamination in the food chain and its risk assessment of populations residing in the Mekong River basin of Cambodia. J Hazard Mater. 262:1064-71 Pryce TO and N Surapol. 2009. Smelting Iron from Laterite: Technical Possibility or Ethnographic Aberration? Asian Perspect 48 (2): 249-264. Available from: https://www.researchgate.net/publication/254927735_Smelting_Iron_from_Laterite_Technica l_Possibility_or_Ethnographic_Aberration [accessed Oct 19 2017]. Ravenscroft P, H Brammer, K Richards. 2009. Arsenic Pollution: A Global Synthesis. WileyBlackwell. 618 p. Rice News. Dec. 12, 2012. Head of Iran's Rice Guild Association said on December 8th that imported Indian rice may be contaminated with chemicals like arsenic. Available at: Http://www.enterisi.it/upload/enterisi/gestionedocumentale/RiceNews43_784_7424.pdf Roberts LC, Hug SJ, Dittmar J, Voegelin A, Saha GC, Ali MA, Badruzzaman AB, Kretzschmar R 2007. Spatial Distribution and Temporal Variability of Arsenic in Irrigated Rice Fields in Bangladesh. 1. Irrigation Water. Environ Sci Technol. 2007 Sep 1;41(17):5960-6 Sampson ML, Bostick B, Chiew H, Hagan JM, Shantz A. 2008. Arsenicosis in Cambodia: Case studies and policy response. Appl. Geochem. 23:2977–2986. Sauve S. 2014 Time to revisit arsenic regulations: comparing drinking water and rice. BMC Public Health201414:465. https://bmcpublichealth.biomedcentral.com/articles/10.1186/14712458-14-465. Stolz JF, P Basu, JM Santini, and RS Oremland. 2006. Arsenic and selenium in microbial metabolism. Annu Rev. Microbiol. 60:107-30. Tanaka, A and S. Yoshida. 1970. Nutritional disorders of the rice plant In Asia. Int. Rice Res. Inst. Tech. Bull. 10. Available at: http://pdf.usaid.gov/pdf_docs/PNAAE432.pdf Thermo Fisher Scientific Niton Analyzers XL3 Analyzer Version 7.0.1 User’s Guide Version C, 2010. 650 pp Vibol S, Hashim JH, Sarmani S. 2015, Neurobehavioral effects of arsenic exposure among secondary school children in the Kandal Province, Cambodia. Environ Res 137:329-337. DOI:10.1016/j.envres.2014.12.001 Unicef 2009. Arsenic in Cambodia. http://www.unicef.org/cambodia/As_Mitigation_in_Cambodia_2009.pdf US EPA 1994. Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma-Mass Spectrometry. Available at: https://www.epa.gov/sites/production/files/201508/documents/method_200-8_rev_5-4_1994.pdf 31

US FDA 2016. Questions & Answers: Arsenic in Rice and Rice Products. Available at: http://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm319948.htm Yin X, Wang L, Zhang Z, Fan G, Liu J, Sun K, Sun GX. 2017. Biomethylation and Volatilization of Arsenic by Model Protozoan Tetrahymena pyriformis under Different Phosphate Regimes. Int J Environ Res Public Health. 2017 Feb 14;14(2). pii: E188. doi: 10.3390/ijerph14020188. Zhang S-Y, PN Williams, J Luo, Y-G Zhu. 2017. Microbial mediated arsenic biotransformation in wetlands. Front. Environ. Sci. Eng., 2017, 11(1): 1. DOI: 10.1007/s11783-017-0893-y. Available at: https://www.researchgate.net/publication/311362159_Microbial_mediated_arsenic_biotransfo rmation_in_wetlands

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