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Organophosphorus and Organochlorine Pesticides Bioaccumulation by Eichhornia crassipes in Irrigation Canals in an Urban Agricultural System a
b
c
a
B. M. Mercado-Borrayo , Silke Cram Heydrich , Irma Rosas Pérez , Manuel Hernández Quiroz a
& Claudia Ponce De León Hill a
Facultad de Ciencias, Universidad Nacional Autónoma de México, Delegación Coyoacán, D.F., México b
Instituto de Geografía, Universidad Nacional Autónoma de México, Delegación Coyoacán, D.F., México c
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Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Delegación Coyoacán, D.F., México Published online: 15 May 2015.
To cite this article: B. M. Mercado-Borrayo, Silke Cram Heydrich, Irma Rosas Pérez, Manuel Hernández Quiroz & Claudia Ponce De León Hill (2015) Organophosphorus and Organochlorine Pesticides Bioaccumulation by Eichhornia crassipes in Irrigation Canals in an Urban Agricultural System, International Journal of Phytoremediation, 17:7, 701-708, DOI: 10.1080/15226514.2014.964841 To link to this article: http://dx.doi.org/10.1080/15226514.2014.964841
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International Journal of Phytoremediation, 17: 701–708, 2015 C Taylor & Francis Group, LLC Copyright ISSN: 1522-6514 print / 1549-7879 online DOI: 10.1080/15226514.2014.964841
Organophosphorus and Organochlorine Pesticides Bioaccumulation by Eichhornia crassipes in Irrigation Canals in an Urban Agricultural System 3 ´ ´ B. M. MERCADO-BORRAYO1, SILKE CRAM HEYDRICH2, IRMA ROSAS PEREZ , MANUEL HERNANDEZ ´ HILL1 QUIROZ1, and CLAUDIA PONCE DE LEON 1
Facultad de Ciencias, Universidad Nacional Aut´onoma de M´exico, Delegaci´on Coyoac´an, D.F., M´exico Instituto de Geograf´ıa, Universidad Nacional Aut´onoma de M´exico, Delegaci´on Coyoac´an, D.F., M´exico 3 Centro de Ciencias de la Atm´osfera, Universidad Nacional Aut´onoma de M´exico, Delegaci´on Coyoac´an, D.F., M´exico
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A natural wetland in Mexico City Metropolitan Area is one of the main suppliers of crops and flowers, and in consequence its canals hold a high concentration of organochlorine (OC) and organophosphorus (OP) pesticides. There is also an extensive population of water hyacinth (Eichhornia crassipes), which is considered a plague; but literature suggests water hyacinth may be used as a phytoremediator. This study demonstrates bioaccumulation difference for the OC in vivo suggesting their bioaccumulation is ruled by their log Kow, while all the OP showed bioaccumulation regardless of their log Kow . The higher bioaccumulation factors (BAF) of the accumulated OC pesticides cannot be explained by their log Kow , suggesting that the OC pesticides may also be transported passively into the plant. Translocation ratios showed that water hyacinth is an accumulating plant with phytoremediation potential for all organophosphorus pesticides studied and some organochlorine pesticides. An equation for free water surface wetlands with floating macrophytes, commonly used for the construction of water-cleaning wetlands, showed removal of the pesticides by the wetland with room for improvement with appropriate management. Keywords: wetland, organochlorine pesticides, organophosphorus pesticides, Eichhornia crassipes, phytoremediation, Xochimilco
Introduction The Mexico City basin was once a beautiful compound of lakes fed by springs and rivers from the surrounding mountains. The Xochimilco canal system is a part of what remains of that great lake system and it is only about 15% of the original Xochimilco Lake, currently located in the southern eastern part of Mexico City about 23 kilometers from the historic city center Its aquifers have been exploited to supply water for the mega city; therefore, to avoid complete dryness of the lake, and as a solution to the management of waste water coming from three main Waste Water Plants, the water from these treatment plants has been dumped into the canals since 1970 and only about 2% infiltrates into the aquifers; thus, the majority of the water remains in the canals untreated. Yet the canal system is an important agricultural area where the canals are used for irrigation of
´ Hill, FacAddress correspondence to Claudia Ponce de Leon ´ ultad de Ciencias, Universidad Nacional Autonoma de M´exico, Cd. Universitaria, Col. Copilco el Bajo, Coyoac´an, C.P. 04510, M´exico, D.F., M´exico. E-mail:
[email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/bijp.
vegetables, flowers and other crops. The area also provides environmental services for the Mexico City metropolitan area and is a habitat for migratory birds. The intensive agriculture has caused pollution by pesticides, even from the banned organochlorine pesticides, and this threatens the edible crops and the regional fauna (Robles-Mendoza et al. 2009). Therefore, achieving good water quality in the canals is of great importance. Processes for pesticide removal have included ozone oxidation (Chen et al. 2013), the Fenton process (Li et al. 2009), membrane processes (Plakas and Karabelas 2012) and biological processes (Shawaqfeh 2010). However, in recent decades, seeking to minimize costs, new technologies have been developed for the removal of pollutants. These emerging technologies focus more on low-scale processes or on local treatments in isolated populations. Some of them adapt conventional methods, such as adsorption with more affordable materials, such as the water hyacinth (Eichhornia crassipes), which is considered to be bio-adsorbent and which has been used to prepare activated carbon for the removal of malathion (Malik 2007), an organophosphate pesticide. Water hyacinth in vivo, too, has demonstrated considerable ability to absorb and concentrate a range of pollutants. The Xochimilco canals suffer from water hyacinth infestation, which is constantly removed and is regarded as a
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702 pest. Nevertheless, it could absorb contaminants present in the canals. Wetlands with Eichhornia crassipes have shown to be better phytoremediators than with other aquatic plants (Farid et al. 2014). It has been shown to remove in vivo many inorganic pollutants, such as Al3+, As3+, Cd2+, Co2+, Cr6+, Cu2+, Fe3+, Mn2+, Ni2+, Pb2+, Sn4+, Sb3+, Ti4+, V5+ and ´ Zn2+ (Jayaweera et al. 2008; Ibrahim et al. 2009; Carrion et al. 2012), and at the laboratory level to remove cyanide, Ag1+, Se4+, Hg2+, Au3+, U6+, Sr2+ and Eu3+ (Ebel, Evangelou and Schaeffer 2007; Malik 2007). In the laboratory it can also absorb organic compounds, such as methylene blue (ElKhaiary 2007), naphthalene (Nesterenko-Malkovskaya et al. 2012), phenol (Wolverton and McKown 1976), diphenamid (Bigham and Shaver 1977), and the pesticide ethion (Xia and Ma 2006). However, no studies have considered accumulation of pesticides in situ in contaminated waters where competition or inhibition from other pollutants may occur. Furthermore, phytoremediation is site-specific (Susarla, Medina and McCutcheon 2002) adding to the importance of studying the uptake of pesticides by the plants in their particular environment. This paper explores the bioaccumulation of organochlorine pesticides (OC) and organophosphorus (OP) with Eicchornia crassipes and its possible role as a phytoremediator in the wetland canals.
Materials and Methods Sampling Sampling consisted in the collection in late February 2013 of water and water hyacinths (aerial and root portion) in five sites in the area with differing land use: Cattle, Urban, crop plants and recreational gardens (Agricultural area I), greenhouses (Agricultural area II), and Conservation. A 1L sample (in duplicate) of water was taken at an approximate depth of 5 cm (the average depth at which the E. crassipes root develops), at each of the selected sites. Each water sample was collected in an amber glass bottle, which was kept at 5ºC prior to analysis. Within 3 hours of arriving to the laboratory, the water samples were filtered with 0.22 μm (nitrocellulose Millipore) membranes and spiked with approximately 100 mL of hexane (HPLC, J.T. Baker) for conservation and cooled to 4◦ C until analyzed. For the water hyacinth, a simple, random sampling in a 20 m radius was performed at each of the selected sites, collecting a sub-population of approximately 40 plants in each site. In the collection, the size and weight of the plants were not considered, in order to prevent any bias based on the morphology of the plant. The plants were collected by hand and transported to the laboratory in coolers lined with aluminum foil. The root and the aerial portion, which includes the reduced stem, the petioles, the leaves and the primary meristems of the water hyacinth, were separated, washed in a methanol solution in order to rinse the adhered pesticide to roots and aerial part, and cut with a clean, new stainless steel blade into pieces of < 2 cm2.
B. M. Mercado-Borrayo et al. Pesticide Extraction Extraction from Water The determination of the pesticides in the water matrix was performed with a liquid-liquid extraction, where 50 mL of the water sample were transferred to a separation funnel, 30 mL of hexane were added and two extraction steps were performed. In order to remove any water, the organic phase was passed through a glass column that contained 2 g of anhydrous sodium sulfate. Once dry, the organic phase was concentrated in the rotary evaporator (LABOROTA 4011) to 3 mL. The pesticides were then quantified by gas chromatography (GC/ECD Agilent Technologies 6890 N) with NPD detector for the organophosphorus pesticides and electron capture detector for the organochlorine pesticides. Chromatography for the organophosphorus pesticides used a 30 m × 0.25 mm × 0.25 μm HP-5 column. The injector temperature was 250◦ C. The detector temperature was 300◦ C. The oven program: 120◦ C for 1 min, then rising by 5◦ C per min to 200◦ C, remaining for 2 min, then rising by 2◦ C per min to 205◦ C, remaining there for 1 min, and finally rising to 300◦ C for 5 minutes to remove impurities from the column. For the 35 min analysis, 2 μL was injected with the auto-sampler in split-splitless mode. Chromatography for the organochlorine pesticides also used a 30 m × 0.25 mm × 0.25 μm HP-5 column. The injector temperature was 300◦ C. The detector temperature was 300◦ C. The oven program: 80◦ C to 190◦ C rising by 20◦ C per min remaining for 1 minute, subsequently rising the temperature to 243◦ C at 2◦ C per min remaining for 1 minute and finally raising the temperature to 300◦ C at 30◦ C per min and remaining for 5 minutes to get any impurities out of the column. For the 46 min analysis, 1 μL was injected with the auto-sampler in split-splitless mode. Calibration curves and standard addition samples used commercial organochlorine pesticide standards (TCL Pesticides Mix, SUPELCO 4-8913) and commercial organophosphate pesticides (Chlorpyrifos (45395), Diazinon (45428), Ethoprophos (45306), Malathion (36143), Methylparathion (36187) and Omethoate (36181) from Riedel-de Ha¨en, Germany). Extraction from Water Hyacinth Both the aerial part and the root were dried with liquid nitrogen and ground separately into a residue that was further dehydrated in the freeze-dryer (Labcono, Free Zone 4.5). The freeze-dried samples were ground again in an agate mortar to reduce the size of the particles, so as to increase the efficiency of the extraction. Three 2 g composite samples from the resulting powder from roots and from the shoots of the 40 plants from each site were placed in the Greenchem containers of the microwave equipment (CEM brand, MARS-X model), with 25 mL of hexane and a reagent blank. Extraction was performed in a single phase: a maximum energy of 1200 W was used to establish a 25 min waiting period until the extraction temperature (125◦ C) was achieved; this was maintained for 15 min without exceeding a pressure of 200 PSI, and subsequently cooled to room temperature.
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Table 1. Water quality parameters measured in the sampled sites.
pH T (◦ C) Conductivity (μS/cm) TSS (mg/L) DOM (mg/L) Chl A (μg/L) DO (mg/L)
Cattle area
Agricultural area I
Urban area
Agricultural area II
Conservation area
7.95 19.5 1130 16.4 8.8 81.4 1.67
7.96 19.0 867 17.4 10.4 109 4.12
7.76 18.5 917 9.2 9.1 13.5 0.86
7.81 18.9 1046 12.3 16.8 77.2 2.25
7.84 19.2 931 10.4 18.3 74.0 4.57
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TSS: Total suspended solids; DOM: Dissolved organic matter; Chl A: Chlorophyll-a; DO: Dissolved oxygen
The extract was filtered (Grade 5 Whatman filter) and placed in a flat bottom boiling flask to be evaporated in a rotary evaporator (Heidolph, Laborota 4011) to approximately 0.2 mL which was then re-dissolved in a 3 mL mixture of HPLC-grade ethyl acetate:hexane 25:75. The extract was cleaned in SPE cartridges (Solid Phase Extraction 1g - 6 mL; StrataTM) previously conditioned with 5 mL of ethyl acetate + 5 mL hexane, then it was eluted with two aliquots of 2 mL from a mixture of ethyl acetate:hexane 25:75.The extract was collected in 10 mL amber glass vials. Last, the resulting 4 mL from the elution were evaporated to a volume of 100 μL with a nitrogen stream. Pesticides were quantified under the same chromatographic conditions as for the water samples. Reagent blanks were treated the same way as the samples.
Results and Discussion General Water Quality Parameters The physicochemical parameters were measured to describe water quality of the different sampled sites, and are presented in Table 1. The pH and the temperature were fairly constant throughout the sites. On the other hand, the rest of the parameters varied in the different sites with no specific trend. Conductivity was the highest in the Cattle area and lowest in the Agricultural area I. Total suspended solids was the lowest in the Conservation area and highest in Agricultural area I. Dissolved organic matter was quite high in Agricultural area II and in the Conservation area, while the rest of the areas were similar. For Chlorophyll-A (Chl-A), the concentrations were similar for all the sites except for the Urban area which
Table 2. Average concentrations of pesticides in water from canals (μgL−1)
Organochlorine pesticides α–BHC β–BHC δ–BHC γ –BHC α–endosulfan β–endosulfan Endosulfan sulfate Aldrin Dieldrin Endrin ketone Heptachlor epoxide DDD Methoxychlor Organophosphate pesticides Chlorpyrifos Diazinon Ethoprophos Malathion Methylparathion
Cattle area
Agricultural area I
Urban area
Agricultural area II
Conservation area
SWa
SWc
log Kow
0.004 0.007 0.022 0.023 ND 0.003 ND 0.070 ND ND 0.003 0.011 0.009
0.010 0.010 ND 0.023 0.009 ND 0.004 0.038 ND 0.137 0.007 0.046 0.015
0.001 0.001 0.608 0.066 ND ND ND 0.892 ND ND ND 0.012 ND
0.002 0.007 ND 0.058 ND ND 0.021 ND ND ND ND 0.028 0.019
0.004 0.008 ND 0.049 ND 0.015 0.041 ND 0.010 ND ND 0.011 0.022
NR NR NR 0.950 0.110 0.110 NR 1.500 0.240 0.086 0.260 0.19 NR
NR NR NR 0.08 0.028 0.028 NR 0.017 0.056 0.036 0.0019 0.011 NR
3.6 3.8 4.1 3.7 4.3 3.5 3.8 6.9 6.2 5.6 3.6 6.5 5.1
0.27 0.11 0.7 0.79 0.43
0.38 0.12 1.23 1.3 0.6
0.19 0.03 0.7 0.73 0.29
ND 0.06 ND ND ND
0.46 0.16 1.71 1.96 0.51
0.083 0.17 NR NR NR
0.041 0.17 NR 0.1 NR
4.7 3.3 3.0 2.7 3.5
ND: not detected; NR: not reported; SWa: Surfacae water acute damage (NOAA. 2008); SWc: Surface water chronic damage (NOAA. 2008); Kow : water–octanol partition coefficient. Pesticides not detected were: Heptachlor, Endrin, Endrin aldehyde, DDT and Omethoate. All RSDs lower than 17% with n = 3.
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Table 3. Average pesticide concentrations in water hyacinth (μgKg−1 dry weight) Cattle area
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LD
Root
Organochlorine pesticides α–BHC 0.013 ND β–BHC 0.014 7.14 δ–BHC 0.016 34.28 γ –BHC 0.050 ND β–endosulfan 0.090 ND Heptachlor epoxide 0.006 48.19 DDT 0.040 5.81 Organophosphate pesticides Chlorpyrifos 0.448 22.84 Diazinon 2.036 6.99 Ethoprophos 0.707 ND Malathion 0.395 72.48 Methylparathion 0.565 17.73 Omethoate 9.020 1052.67
Agricultural area I
Agricultural area II
Urban area
Conservation area
Aerial
Root
Aerial
Root
Aerial
Root
Aerial
Root
Aerial
0.82 14.06 27.63 ND ND 16.82 4.34
ND 2.62 8.32 ND ND 18.92 1.42
ND 17.89 11.16 ND 17.45 17.81 ND
ND 65.75 ND 83.32 ND 259.64 ND
ND 56.96 58.56 92.33 165.55 52.20 ND
ND ND 25.79 ND ND 65.74 ND
ND 25.49 27.81 35.93 ND 38.59 ND
ND ND 22.79 ND ND 54.73 ND
ND 16.12 ND 51.66 54.73 ND ND
16.04 5.6 50.04 47.68 25.81 46.96
28.5 22.85 ND 74.35 21.15 1581.44
10.57 2.03 29.79 31.08 16.07 19.57
9.79 5.53 ND 27.16 11.05 381.58
4.9 1.2 22.71 22.23 8.34 5.7
12.7 11.77 717.78 39.82 14.63 1.45
12.26 5.12 ND 42.87 13.66 623.72
18.04 11.64 62.76 58.48 15.56 ND
17.23 7.06 44.99 59.56 20.12 575.88
ND: Not Detected; LD: Detection Limit in the plant (μgKg−1); Organochlorine pesticides not detected are: α–endosulfan (LD: 0.010 μg Kg−1), Endosulfan sulfate (LD: 0.051 μgKg−1), Aldrin (LD: 0.005 μgKg−1), Dieldrin (LD: 0.461 μgKg−1), Endrin (LD: 0.059 μgKg−1), Endrin ketone (LD: 0.059 μgKg−1), Heptachlor (LD: 0.006 μg Kg−1), Endrin aldehyde (LD: 0.057 μgKg−1), DDD (LD: 0.010 μgKg−1) and Methoxychlor (LD: 0.007 μgKg−1). All RSDs lower than 21% with n = 3.
was lower. The lower content of Chl-A in this site could be explained by the little light entering the water as it is constantly lined with water hyacinth. Chlorophyll-A was determined to characterize de primary production of the sites and possibly relate them to xenobiotics degradation. In general, dissolved oxygen was low in the area, with the lowest value in the Urban area. The measured parameters were compared to those
reported by Anderson et al. (2013) in a constructed wetland for the treatment of waste water. Total suspended solids in our study were somewhat higher than their outlet sites but lower than their lagoon values, while their Chl-A was an order of magnitude higher in the lagoon but lower in the outlet than our study. In the other hand dissolved oxygen had comparable values with our study, as were their conductivity values and
Table 4. Bioaccumulation and Translocation factors Cattle area BAF
TF
Organochlorine pesticides α–BHC 2005 ——– β–BHC 3028 0.5 δ–BHC 2814 1.2 γ –BHC ——– ——– β–endosulfan ——– ——– DDT ——– 1.3 Heptachlor 21670 2.9 epoxide Organophosphate pesticides Chlorpyrifos 64 0.7 Diazinon 36 0.8 Ethoprophos 82 ——– Malation 73 0.7 Methyl71 1.5 parthion Omethoate ——– 0.04
Agricultural area I
Agricultural area II
Urban area
Conservation area
BAF
TF
BAF
TF
BAF
TF
BAF
TF
——– 2051 ——– ——– ——– ——– 5247
——– 0.1 0.7 ——– ——– ——– 1.1
——– 12271 96 2661 ————————–
———1.2 ——– 0.9 ——– ——– 4.9
——– ——– 3643 619 ——– ——– ——–
——– ——– 0.9 ——– ——– ——– 1.7
——– 2015 ——– 1054 3549 ——– ——–
——– ——– ——– ——– ——– ——– ——–
115 193 122 84 85
0.4 0.1 ——– 0.4 0.8
91 214 82 89 88
0.5 0.2 ——– 0.8 0.8
——– 290 ——– ——– ——–
1.0 0.4 ——– 1.1 0.9
0.4 0.3 ——– 1.3 0.6
1.0 0.6 0.7 1.0 1.3
——–
0.01
——–
0.01
——–
429.0
——–
——–
BAF: Bioaccumulation factor TF: Translocation factor.
Pesticides Bioaccumulation by Eichhornia crassipes their pH in the outlet. Hence, the physicochemical parameters of our sites seem to be that of half-way treated water in a constructed waste water treatment wetland.
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Organochlorine and Organophosphorus Pesticides in the Canal Water The concentration of organochlorine and organophosphate pesticides in the water collected at the five sites is shown in Table 2. The organochlorine pesticides not detected in any of the sites were DDT, heptachlor, endrin, endrin aldehyde, and the organophosphorous pesticide omethoate. The lack of the first three and the presence of their metabolites suggest they have not been recently applied in the area. The rest of the organophosphorus pesticides were detected in all but one site. The highest concentrations of the organochlorine pesticides were found in the Urban area and the organophosphorus pesticides in the Conservation area. The pesticides that exceeded the values established by the National Ocean and Atmosphere Administration (NOAA 2008) for superficial water concentrations leading to acute damage were endrin ketone and chlorpyrifos; those that exceeded the concentrations for chronic damage were aldrin, heptachlor epoxide and malathion (Table 2).
Accumulation of Organochlorine and Organophosphorus Pesticides in the Water Hyacinth The analysis of organochlorine and organophosphorus pesticide concentrations (μg/kg) in the aerial portion and the root of the water hyacinth are shown in Table 3. In the aerial portion of the water hyacinth, the most frequent organochlorine pesticide was β-BHC and that with the highest concentration was β-endosulfan. In the root, the pesticide with the greatest frequency and concentration was heptachlor epoxide (Table 3). In both aerial portion and root, the organophosphorus pesticide with the greatest frequency and concentration was omethoate. The Urban area had the greatest concentration of organochlorine pesticides, and Agricultural area I had the greatest concentration of organophosphorus pesticides (Table 3). Figure 1 shows that most pesticides were at higher concentrations in the water hyacinth than in the water, suggesting that the plant is accumulating them. Organochlorine pesticides present in the water hyacinth in descending concentration were as follows: BHCs, heptachlor epoxide, β-endosulfan, and DDT. Absent from the plant tissues were α-endosulfan and endosulfan sulfate, aldrins (aldrin, dieldrin, endrine ketone), DDD and methoxychlor pesticides; presumably they were not susceptible to bioaccumulation, since it is unlikely that they had been degraded by the water hyacinth because OC pesticides are very persistent. Rather, this difference in bioaccumulation suggests that bioaccumulation is ruled by their log Kow shown in Table 2. In this sense, an OC with a low octanol-water partition coefficient (Kow ) (more water soluble) would be incorporated into the plant while an OC with a higher Kow (less water soluble) would not. All the OP pesticides were detected in the water hyacinth at higher con-
705 centrations that in the water, thus showing bioaccumulation by the water hyacinth regardless of their log Kow . This is consistent with the concept (Delle 2001; Tournebize et al. 2013) that phyto-uptake of organic pollutants is influenced by their physicochemical characteristics such as the Kow . Uptake is efficient when chemicals are moderately hydrophobic (log Kow 1-3.5), as are the organophosphate pesticides except chlorpyrifos (Table 2). More strongly hydrophobic chemicals (log Kow > 3.5) such as the organochlorine pesticides bind strongly to the roots and therefore are not easily translocated to the aerial part. Water-soluble chemicals (log Kow < 1) are not hydrophobic enough to be sorbed or transported into the plant (Stottmeister et al. 2003).
Bioaccumulation and Translocation Factors The bioaccumulation factor (BAF) is the plant:water concentration ratio of the pollutant. The highest BAF for organochlorine pesticides was for β-BHC followed by heptachlor epoxide, β-endosulfan and γ -BHC; as for organophosphorus pesticides, diazinon had the highest bioaccumulation factor followed by chlorpyrifos, methylparthion, malathion and ethoprophos (Table 4). The bioaccumulation factors are clearly greater for the OC pesticides than for the OP pesticides and cannot be explained by the log Kow of the pesticide since the bioaccumulated OC pesticides have Kow values similar to those of the OP pesticides, hence suggesting that the OC pesticides may also be transported passively into the plant. The translocation factor (TF) is the relationship between the content of the pesticide in the aerial structure and the submerged structure, so that a TF of >1 indicates the mobilization of the pesticide to the aerial tissues, while a TF 1, translocating the pollutant into the aerial part and freeing the roots for more pollutant to be absorbed. Although fewer OCs than OPs accumulated by the plant were translocated into the aerial part, those that had translocation factor were usually greater than those of the OPs (Table 4). Interestingly, the omeothate that was not present in the water, had the highest translocation factor, possibly explained by its high solubility in water. These results suggest that OP bioaccumulation and translocation is guided mainly by hydrophobicity, whereas translocation of OCs is influenced by some other properties as well (e.g., aqueous phase transfer conductivity (Gobas et al. 1991)). A good phyto-remediator has to have good bioaccumulation and be able to translocate the pollutants to the shoots so that more pollutant can be absorbed. In this respect, the organochlorine pesticides with better phytoremediation were heptachlor epoxide > β-BHC > δ-BHC > γ -BHC > β-endosulfan > DDT. The OP pesticide with the best phyto-remediation was surprisingly chlorpyrifos which has the highest log Kow , though if we assumed that omethoate is not present in water because it has been absorbed by the water hyacinth, then this pesticide has the best phytoremediation.
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Fig. 1. Organochloride families and organophosphate pesticides concentrations (ugKg−1) in water and hyacinth in the sampled sites.
Fig. 2. Localization of sites used in the assessment of the wetland system.
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Prototype of a Wetland Cell for Water Treatment Observations of the wastewater depuration capacity of natural wetlands have led to a greater understanding of the potential of these ecosystems for pollutant assimilation and have stimulated the development of artificial wetland systems for treatment of wastewaters from a variety of sources. However, natural wetlands are still important in the improvement of water quality as they act as buffer zones surrounding water bodies and are able to efficiently remove many pollutants (Anderson et al. 2013; Pierbon et al. 2013; Tournebize et al. 2013). Wetlands are complex mosaics of water panels, submerged vegetation, floating vegetation and emerging vegetation, where the phreatic level must be close to the surface and the ground remains saturated with water for a long period of every year (Russo 2008). This definition applies to our study area. The typical vegetation includes reeds, rushes, water lentils and, mainly, water hyacinth. In an attempt to estimate whether this wetland can function as a free water surface wetland with a floating macrophyte system, an equation commonly used for the construction of water-cleaning wetlands (USEPA EPA/625/1-88/022 1998) was used. This equation has been used for conventional pollutants such as biochemical oxygen demand or nitrogen, although not hitherto for more complex pollutants. We used it to assess our wetland system as the equation does not include any term specific to a pollutant. Since the wetland is already present, the equation helped us to determine the efficiency with which the wetland should be dealing with the pesticides studied, and compare it with the experimental data. Theoretical and experimental ratio of the pesticide concentrations entrance/exit were calculated and measured, respectively, for a section of the canals going from their probable source toward the exit of the water from the canals. An experimental ratio greater or equal to the theoretical value would indicate high removal and hence an efficient water-treatment wetland (USEPA EPA/625/1-88/022 1998). The proposed routes are from Agricultural Area I to the Conservation Area (OC Segment) for organochlorine pesticides and from Agricultural area II to the Cattle Area for organophosphorus pesticides (OP Segment) depicted in Figure 2. The Agricultural Area I was considered the entry of the OC pesticides to the system since it is where pesticides are mostly applied in a variety of crops and gardens, whilst Agricultural area II are mostly greenhouses with flowers where ´ abundant OP pesticides are applied (Alcantara-Concepcion 2014) and the Conservation and Cattle areas are closest to the water exit. The segments chosen were roughly the same area. The theoretical ratio was obtained combining wetland equations (Crites, Sherwood and Middlebrooks 1998) (Kadlec and Knight 1995) giving Equation 1. As =
Qln (CO /Cf ) KT (y) (n)
where the ratio of pesticides can be calculated as follows: ln(CO /Cf ) =
(y) (n) (As ) KT Q
(1)
where: Co : Initial concentration of pesticides (μg/L) Cf : Final pesticides concentration toward the exit effluent (μg/L). y: system average depth = 2 m n: porosity of the wetland silt = 0.05 As : segment area1400 m long x 8 m wide = 11200 m2 Q: is the flow = 34,128 m3/d KT : Reaction velocity constant modified to the temperature of our system (◦ T = 19.45◦ C average of the historical data) in Eq. (2). KT = k2o (1.06◦ )T−20
(2)
Where the value k20 is 1.104 d−1 the value commonly used for the treatment of waste water through wetlands (Crites, Sherwood, and Middlebrooks 1998). K19.45 = 1.104 (1.06)19.45−20 = 0.92 d −1 The optimum theoretical removal of pesticides by the water hyacinth system according to Equation (1) Co /Cf is 1.030 for organochlorine and 1.035 for organophosphorus pesticides. When the removal of the sum of the OC and OP pesticides is determined from the sites allegedly near the sources and the sites near the water exit from the canals, the experimental Co /Cf is 6.48 for organochlorine pesticides and 1.03 for organophosphorus pesticides. These numbers show a good removal of the OC pesticides while the experimental data for the OP pesticides barely equal the theoretical value, indicating that there is not an optimal removal of the pesticides from the system; in fact, the OP concentrations in the different sites indicate diffuse sources rather than one source. These numbers are promising since remediation of the pesticides could probably be optimized with appropriate management of the wetland, more specifically with appropriate management of the water hyacinth, as it is the main aquatic plant and the young plants are better phytoextractor than older plants(El-Gendy 2008; Prasertsup and Ariyakanon 2011) and population density can hinder uptake of organic pollutants(Dosnon-Olette et al. 2010); therefore constant removal of the water hyacinth from the canals could probably enhance the removal of the pesticides.
Conclusions The bioaccumulation data for the organochlorine pesticides, suggests bioaccumulation is ruled by their log Kow ; while the organophosphorus pesticides do not indicate bioaccumulation differences in their log Kow range. The bioaccumulation and translocation factors for the water hyacinth show it is a good phytoremediator with certain organochlorine and organophosphorus pesticides in the wetland. The organochlorine pesticides with best phytoremediation were heptachlor epoxide > β-BHC > δ-BHC > γ -BHC > β-endosulfan > DDT. The OP pesticide with the best phyoremediation is omethoate if we assume that all the omeathate
708 has been absorbed by the water hyacinth. The construction water-cleaning wetland design equations for a sub-superficial wetland used to assess the wetland revealed good removal of the OC pesticides while the data for the OP pesticides indicates that there is not an optimal removal of the pesticides from the system; rather, the OP concentrations in the different sites indicate diffuse sources. Our results demonstrated that water hyacinth has an environmental service and that constant removal of the water hyacinth from the canals could probably enhance the removal of the pesticides.
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Acknowledgments B. M. Mercado-Borrayo gratefully acknowledges the “Programa de Becas Posdoctorales de la Universidad Nacional ´ Autonoma de M´exico, UNAM”.
Funding The authors thank DGAPA, UNAM for the financial support through Project PAPIME 205013.
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