Environ Geochem Health (2008) 30:21–30 DOI 10.1007/s10653-007-9104-2
ORIGINAL PAPER
Total mercury and methylmercury concentrations in fish from the Mojana region of Colombia Jose´ Marrugo-Negrete Æ Jesus Olivero Verbel Æ Edineldo Lans Ceballos Æ Luis Norberto Benitez
Received: 5 December 2006 / Accepted: 3 April 2007 / Published online: 3 July 2007 Springer Science+Business Media B.V. 2007
Abstract Total mercury (T-Hg) and methylmercury (MeHg) concentrations have been measured in the muscle tissue of 16 fish species consumed in the Mojana region of Colombia. T-Hg analysis was performed by cold-vapor atomic-absorption spectroscopy (CV-ASS) and MeHg analysis by gas chromatography with electron-capture detection. Higher T-Hg and MeHg concentrations were detected in carnivorous species (T-Hg = 0.371 ± 0.172 (mg g 1 fresh wt, MeHg = 0.346 ± 0.171 mg g 1 fresh wt) than in non-carnivorous fish (T-Hg = 0.155 ± 0.108 mg g 1 fresh wt, MeHg = 0.146 ± 0.102 mg g 1 fresh wt). In the different species mercury was present almost completely as the methylated form, with percentages between 80.5 and 98.1% (mean 92.0 ± 3.4%). In 13.5% of fish-tissue samples T-Hg concentrations exceeded the maximum level recommended by the World Health Organization for human consumption J. Marrugo-Negrete (&) E. L. Ceballos Environmental and Analytical Chemistry Group, University of Cordoba, Grupo de Quı´mica Analı´tica y Ambiental, Carrera 6, No. 76-103, Monteria, Colombia e-mail:
[email protected] J. O. Verbel Environmental and Computational Chemistry Group, University of Cartagena, Campus de Zaragocilla, Cartagena, Colombia L. N. Benitez Department of Chemistry, Universidad del Valle, A.A. 25360 Cali, Colombia
(Hg = 0.5 mg g 1 fresh wt). Although mean T-Hg concentrations in all fish samples (0.269 ± 0.181 mg g 1 fresh wt) did not exceed this limit, risk assessment suggested that the consumption of 0.12 kg fish day 1 could increase the risk of mercury poisoning of the inhabitants of this region.
Keywords Mercury Methylmercury Mercury in fish Mercury risk Mojana Colombia
Introduction Mercury is one of the metals with the greatest effect on aquatic ecosystems. It may occur in the environment either naturally or as a result of anthropogenic activity, and cause irreversible damage to aquatic and terrestrial biota (Uryu et al. 2001). In Colombia, metallic Hg is directly incorporated into aquatic ecosystems and the atmosphere as a result of extraction of gold, and there have been no previous attempts to recover the metal. In this regard, from 1987 to 1997 an estimated 240 tons of mercury were released into the environment (Malm 1998). When the residues from the gold-extraction process reach rivers or marshes they carry large quantities of mercury. In aqueous environments, inorganic mercury is converted into organic mercury compounds by a variety of microorganisms, mainly sulfur-reducing forms of anaerobic bacteria (WHO 1990; Gilmour &
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Henry 1991; Jeremiason et al. 2006). These biotransformation processes can occur in the sediment or the water column (EPA 2001). Methylmercury is a stable organic mercury compound and is the most toxic form of mercury in the environment (Jernelov 1973). It is bioaccumulated in fish and biomagnified through the aquatic food chain. Because more than 90% of the mercury in aquatic biota (benthic microorganisms and fish) is present as methylmercury (Lacerda et al. 1994; Morel et al. 1998), the major source of human exposure to methylmercuy is consumption of fish (Kehrig et al. 1998; WHO 1990). For this reason evaluation of mercury levels in fish is an important aspect of evaluating the potential effect of the metal on public health. Although there is evidence that gold-mining activity contaminates ecosystems in the north of Colombia (Olivero & Solano 1998; Olivero et al. 1997), few studies have evaluated the effect of contamination with mercury of aquatic biota of the Mojana region, which is regarded as extremely rich in biodiversity. High T-Hg concentrations have been found in aquatic plants, sediments, and fish in the municipality of Caimito in this region (Olivero et al. 2004). The purpose of this study was to evaluate, for the first time, T-Hg and MeHg concentrations in the predominant fish species consumed in the Fig. 1 The Mojana region (Colombia). Municipalities: 1. Ayapel, 2. San Marcos, 3. Caimito, 4. San Benito, 5. Sucre, 6. Majagual, 7. Guaranda, 8. San Jacinto, 9. Achi, 10. Magangue
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municipalities of the Mojana region and to ascertain potential human exposure to mercury from fish consumption. This study identifies the most contaminated species and it reports statistical correlations between tissue concentration and length of the fish.
Materials and methods Area of study The Mojana region is located in northwest Colombia (Fig. 1). It has an area of 5,545 km2, a population of 316,320 (DANE 1999), and contains the municipalities Achi, Ayapel, Caimito, Guaranda, Majagual, San Benito, San Marcos, Magangue, San Jacinto, and Sucre. The region is surrounded by three rivers, the Magdalena, Cauca, and San Jorge, and is crossed by channels that drain the area during flood periods, which occur mainly in the west region, in the San Jorge river basin. During the rainy season (July– December) it receives mercury-polluted input from the Cauca river, in particular, because this river carries gold-mining residues from the largest mining zone in Colombia, the south of Bolivar and northeast Antioquia, where mercury has contaminated the ecosystems (Olivero & Johnson 2003). Because of the close proximity to the gold mining area,
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atmospheric Hg can be also deposited as both dry or wet deposition. The dominant climate is hot and humid, and temperature varies between 28 to 338C. The most important economic activities in the region are agriculture, cattle raising, and fishing, the last with production of 9691 tons in 2000 (CEER 2004). The species with the main contribution to income from fishing in the region are Prochilodus magdalenae (bocachico), Pseudoplatystoma fasciatun (bagre pintao), Caquetaia krassi (mojarra amarilla), Sorubin cuspicaudus (blanquillo), Hoplias malabaricus (moncholo), Plasgioscion surinamensis (pacora), Ageneiosus caucanus (doncella), and Leporinus muyscoruma (liseta). Fish sampling and analysis Fish were collected between May and August 2005 during fishing campaigns with local fishermen. Sampled species (Table 1) included those regarded the most important to the population’s diet. After Table 1 T-Hg concentrations in fish (mg g Common name
1
measurement of length, the fish were eviscerated, placed individually in plastic bags, labeled, and transported on ice to the laboratory. Samples for analysis were obtained from dorsal muscle dissected with a plastic knife and analyzed fresh. A total of 237 specimens from 16 species were collected with the help of fishermen from the municipalities of Ayapel, Caimito, Guaranda, Majagual, Sucre, San Marcos and San Benito, representing the entire region. All samples were analyzed for T-Hg and 128 were analyzed for MeHg. T-Hg analysis was performed by cold-vapor atomic-absorption spectroscopy (CV-AAS) after acid digestion of the sample with 2:1 v/v H2SO4 HNO3 at 100–1108C for 3 h (Sadiq et al. 1991). MeHg analysis was performed by gas chromatography with electron-capture detection (PNUMA/FAO/OIEA 1987). Briefly, 0.2–0.3 g fish was digested with 2.8 mL HCl, 2.0 g NaBr, and 14 mL toluene. The mixture was vortex mixed for 15 min then centrifuged. A solution of cysteine (1.4% w/v, 6.0 mL) was added, and after mixing and
fresh wt) captured in the Mojana region, Colombia
Scientific name
Typea
T-Hg, m ± sb
T-Hg, range
Length range (cm)
nc
%
Mojarra amarilla
Caquetaia kraussi
C
0.390 ± 0.203
0.101–0.816
10.5–21.1
29
Doncella
Ageneiosus caucanus
C
0.512 ± 0.158
0.267–0.996
22.0–36.1
19
12.2 8.0
Bagre pintao Blanquillo
Pseudoplatystoma fasciatun Sorubin cuspicaudus
C C
0.413 ± 0.085 0.465 ± 0.091
0.279–0.521 0.365–0.689
34.7–43.1 32.0–46.5
11 13
4.6 5.5
Moncholo
Hoplias malabaricus
C
0.278 ± 0.155
0.107–0.669
18.4–26.1
21
8.9
Pacora
Plagioscion surinamensis
C
0.307 ± 0.126
0.121–0.612
19.1–34.2
16
6.8
Rubio
Salminus affinis
C
0.279 ± 0.026
0.237–0.301
21.2–24.3
5
2.1
Barbudo negro Yalu´a
Rhamdia sebae
C
0.395 ± 0.217
0.158–0.585
17.2–23.0
3
1.3
Cyrtochorax magdalenae
C
0.183 ± 0.044
0.143–0.279
20.1–25.0
8
3.4
Mean (C)
0.371 ± 0.172
0.101–0.996
10.5–46.5
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52.7 14.3
Bocachico
Prochilodus magdalenae
NC
0.106 ± 0.057
0.035–0.218
15.8–26.8
34
Arenca
Tripotheus magdalenae
NC
0.341 ± 0.106
0.181–0.436
13.0–14.3
7
2.9
Liseta
Leporinus muyscoruma
NC
0.245 ± 0.129
0.072–0.586
16.0–27.2
24
10.1
Cacucho
Panaque gibbosus
NC
0.182 ± 0.036
0.148–0.245
18.0–23.1
6
2.5
Gurami
Trichogaster sp.
NC
0.043 ± 0.004
0.036–0.049
10.8–12.6
8
3.4
Viejito Vizcaı´na
Curimata magdalenae
NC
0.092 ± 0.039
0.041–0.240
10.0–12.2
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9.7
Curimata mivartii
NC
0.186 ± 0.025
0.163–0.247
18.9–21.4
10
4.2
Mean (NC)
0.155 ± 0.108
0.035–0.436
10.0–26.8
112
Total
0.269 ± 0.181d
0.035–0.996
10.0–46.5
237
a
47.3 100
C, carnivorous; NC, non-carnivorous
b
Mean ± standard deviation
c
Number of specimens
d
Significant differences between mean T-Hg values for different species (ANOVA, P < 0.01)
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centrifugation the organic phase was removed. The aqueous phase was combined with 1.2 mL 6 mol L 1 HCl, 0.5 g NaBr, and 4 mL toluene, vortex mixed and centrifuged, the aqueous layer was discarded, and 5 mL of the toluene layer injected into the gas chromatograph (Model PE Autosystem XL). The temperature of the column was kept at 1008C for 1 min then programmed at 58 min 1 to 1408C which was maintained for 4 min. Compounds were separated on a 30 m · 0.53 mm i.d. megabore capillary column coated with RTX-1701 (14% cyanopropylphenyl, 86% dimethylpolysiloxane); the carrier gas was He at 8 mL min 1 and the make-up gas was N2 at 45 mL min 1. The injector and detector temperatures were 140 and 2408C, respectively. The accuracy of the methods was quantified by analysis of blanks, calibration standards, spiked samples, and the certified material DORM-2, dogfish muscle, from the National Research Council of Canada. The measured concentration of T-Hg in DORM-2 was 4.46 ± 0.25 mg g 1 (certified value 4.47 ± 0.32 mg g 1); that for MeHg was 4.09 ± 0.33 mg g 1 (certified value 4.47 ± 0.32 mg g 1). Mean recovery of T-Hg and Me-Hg from spiked samples was 95.2 ± 4.3 and 93.2 ± 4.2% (n = 6), respectively. Method precision, measured as the relative standard deviation, was always
