IUCN Otter Specialist Group . . . leading global otter conservation Last Update: Friday November 23, 2018
 
 
[Home]

Volume 8 Pages 1 - 47 (February 1993)

Citation: Gutleb, A.C., Schenck, C. & Staib, E. (1993) Total Mercury and Methylmercury Levels in Fish from the Department Madre de Díos, Peru. IUCN Otter Spec. Group Bull. 8: 16 - 18

Previous | Contents | Next

Total Mercury and Methylmercury Levels in Fish from the Department Madre de Díos, Peru

Arno C Gutleb1, Christof Schenck and Elka Staib2

1Institute for Medical Chemistry, University of Veterinary Medicine, Linke Bahngasse 11, A-1030 Vienna. Austria
2Wildsbiologische Gesellschaft München, Postfach.170, D-8103 Oberammergau, Germany

Abstract: Very little is known about environmental contamination in most otter species.  In the range of the Giant Otter, Pteronura brasiliensis, gold miners discharge a great deal of methylmercury into the environment, and this is known to biomagnify in the food chain.  Assays for methylmercury were carried out on fish collected in the Madre de Dios department of Peru, from near gold mining areas, and also from more than 100km away; additional fish were obtained from fish markets.  Results show that significant contamination occurs in fish bigger than the normal prey size of the otters, but at present, there are low levels in prey species - this should be monitored closely in future.

Despite growing concern and research interest in the contamination of otters and their food in Europe and North America (Lutra lutra and Lutra canadensis), very little is known about levels of hazardous substances in otters from other areas. In particular it could be of interest whether regions far away from industry and civilisation are contaminated too.

The giant otter Pteronura brasiliensis is categorized as almost extinct in two countries of its original distribution, seriously endangered in seven countries, and widespread only in Surinam and Guyana (Foster-Turley et al., 1990). In 1990 a long term investigation and conservation project on Pteronura brasiliensis was started by Frankfurt Zoological Society and Munich Wildlife Society. As part of the Giant Otter Project fish from the southeast of Peru (see Fig. 1) were analysed for their content of mercury and methylmercury.  In the area of River Madre do Díos there are still huge parts of untouched tropical rainforest, however, local colonization and gold mining have started. Gold occurs as dust in the sediments of-the rivers and after concentration by washing the mixture of sand and gold is treated with mercury for extraction. With data from the "Banco del Minero" we assume the annual mercury discharge to be in the region of about 9000 kg. As methylmercury biomagnifies upward in the foodchain, top level predators such as otters may accumulate mercury up to toxic levels.

Map of South America in Peru near the border with Brazil and Bolivia
Figure 1. Location of the study site (click for larger version)

MATERIAL AND METHOD

All fish were collected in the Department Madre de Dios. They were caught in rivers and lakes close to the gold-mining activity, but also more than 100 km away in virgin areas, and additionally some were bought on local fishmarkets.  Samples were taken from the following fish genera: Potamorhina, Serasalmus, Plagioscion, Prochilodus, Cynodon, Myleus and big catfish like Pseudopimedolus and Pseudoplatystoma.

Muscle samples wore stored either in formalin (10 %) or in absolute ethanol prior to analysis.  Methylmercury was separated following the method of Bender (1989) using toluene as a solvent for the separation of organic from inorganic mercury. The disintegration is done according to the method of Schnitzer et al. (1987) using a microwave disintegrator (Prolabo Microdigest 300). Mercury levels in the solutions were detected by using Hitachi Z-8100 Polarized Zeeman Atomic Absorption Spectrophotometer with a hydride formation system. For proof of the method, total mercury concentration in a reference standard MA-A-2TM (fish), prepared by the IAEA was determined.

RESULTS AND DISCUSSION

The findings for the reference standard were between 90 % end 92 % of the given value. No corrections for mercury concentrations in fish were made.

Mercury levels in those fish which already have been analysed are below 0.2µg/g wet weight (ppm). This is in the range or slightly higher than the mercury level which is assumed to be tolerable for Lutra lutra (Hovens 1992). Six big fish (up to 50 kg) had a total mercury body burden of 0.46 to 1.55 µg/g wet weight which is lower than the levels for walleye (Stizostedion vitreum) reported from a mercury polluted river in Canada (Fimreite et al. 1973). There are many factors influencing the mercury levels in fish e.g. size of watershed, direct atmospheric deposition, local geology (Wren et at. 1988), low calcium level or pH (Wren et al. 1983). The explanation for the levels of mercury in our study might be owing to a combination of some of these factors.

Corresponding to results of Cappon et al. (1981) a similar proportion of methylmercury to mercury (61 to 97 %) in muscle tissues was found.

Considering the limited number of samples, mercury and methylmercury levols seem to be low in some species and within the tolerable range. Fish with high mercury levels (Pseudopimelodus and Pseudoplatystoma) are too big (approximately 50 kg) to be a prey for the otter. After having finished the analysis of all samples a full report including a detailed discussion will be published elsewhere. This report will be available from the authors. Nevertheless, direct mercury discharge in areas with viable otter populations should be strictly controlled or preferably banned completely. Particularly as a subtle effect of low mercury concentrations on sublethal mercurialism; i.e. on reproduction and survival of otter populations, cannot be excluded.

REFERENCES

Bender H.M. (1989). Vorkommen von Quecksilber im Seehund (Phoca vitulina) und in Eiern von Flußseeschwalben. Dissertation. Tierärztliche Hochschule Hannover.
Cappon. C.J., & Smith, J.C. (1981), Mercury and selenium content and chemical form in fish muscle. Arch. Environ. Contam. Toxicol. 10: 306 - 319.
Fimreite, N. & Reynolds, L.M. (1973). Mercury contamination of fish in Northwestern Ontario. J. Wildl. Man. 37: 62-68.
Foster-Turley. P., Macdonald, S.M. & Mason, C.F., Eds (1990). Otters - an action plan for their conservation. IUCN, Gland.
Hovens, J.P.M. (1992). Microvorontreinigingen in waterbodems en visbiota in Nederland; de visotter (Lutra lutra) als normsteller. SON Leeuwarden & Landbouwuniversiteit Wegeningen verslag nr. 3044.
Schnitzer, G., Pellerin, C. & Clouet, C. (1987). The use of microwaves in wet digestion of a biological substance with a view to assay of mercury by atomic absorption spectrometry (AAS)
Wren, C.D. & MacCrimmon. H. (1983). Mercury levels in sunfish relative to lake pH and other environmental variables of Precambian shield lakes. Can. J. Fish, Aquat. Sci. 40: 1737 - 1744.
Wren, C.D. & Stokes, P.M. (1988). Depressed mercury levels in biota from acid and metal stressed lakes near Sudbury, Ontario. Ambio 17: 28-30

Previous | Contents | Next