Biomagnification of DDT through the benthic and pelagic food webs of Lake Malawi, East Africa: importance of trophic level and carbon source.

Lake Malawi, an East African Rift Valley lake, is internationally renowned for having the highest diversity of fish species in the world, and these cichlids are highly specialized in their dietary habits. In this lake, tissue stable carbon (delta13C) and nitrogen (delta15N) isotopes can be used over several trophic levels to distinguish those consumers relying upon carbon fixed by either benthic or pelagic primary producers. As such, it was possible to contrast the biomagnification of persistent organochlorines through the benthic and pelagic food webs. In 1996 and 1997, food-web organisms were collected from Lake Malawi and analyzed for organochlorines, delta13C and delta15N to determine the factors that affectthe biomagnification of contaminants in a tropical lake. The pesticide DDT was the most predominant pollutant in the biota from Lake Malawi and was found at the highest concentrations in the largest and fattiest fish species. As observed in temperate systems, log-transformed sigmaDDT concentrations in food-web organisms were significantly predicted by delta15N or log lipid (r2 = 0.32 and 0.40, respectively). In addition, the slope of the regression of log sigmaDDT versus delta15N was significantly higher in the pelagic than the benthic food web. These results indicate that pelagic organisms are at greater risk of accumulating these pollutants than biota relying upon benthic primary production.

Bioaccumulation of radionuclides in fertilized Canadian Shield lake basins.

Radionuclide tracers of heavy metals (59Fe, 60Co, 65Zn, 75Se, 85Sr, 134Cs and 203Hg) representing potential contamination from nuclear power plants, industry and agriculture were added to separate basins of Lake 226, Experimental Lakes Area, northwestern Ontario. The two basins were part of a eutrophication experiment and differed in their trophic status; the north basin (L226N) was eutrophic whereas the south basin (L226S) was mesotrophic. Our objective was to determine the uptake of the radionuclides by biota and the effect of lake trophic status on their bioaccumulation. The trophic status of the lakes did not appear to have a marked effect on the accumulation of radionuclides by the biota. This may have been because of a mid-summer leakage of nutrients between the basins which enhanced primary production in L226S, because there is a time lag between primary production and the availability of the radionuclides to the fishes or because trophic status does not affect the uptake of at least some of these radionuclides. However, there was a tendency for faster uptake of the radionuclides in L226N by fish than L226S, but the differences were not significant. Concentrations in the biota generally decreased in the order: fathead minnow > pearl dace > tadpoles > slimy sculpin > leeches. Concentrations in biota generally decreased in the order. 65Zn > 203Hg > 75Se > 134Cs > 60Co > 85Sr = 59Fe. Cobalt-60 concentrations in tadpoles were greater than in the other biota. Radionuclide concentrations in the tissues of lake whitefish indicated that uptake was predominantly from food. Radionuclide concentrations were usually higher in the posterior gut, liver and kidney than in other tissues, whereas body burdens were generally high in the muscle for 75Se, 134Cs and 203Hg; kidney and gut for 60Co; and bone for 65Zn and 75Se. Mercury-203 burdens were also high in the bone and gut.

High concentrations of toxaphene in fishes from a subarctic lake.

Concentrations of toxaphene and other organochlorine compounds are high in fishes from subarctic Lake Laberge, Yukon Territory, Canada. Nitrogen isotope analyses of food chains and contaminant analyses of biota, water, and dated lake sediments show that the high concentrations of toxaphene in fishes from Laberge resulted entirely from the biomagnification of atmospheric inputs. A combination of low inputs of toxaphene from the atmosphere and transfer through an exceptionally long food chain has resulted in concentrations of toxaphene in fishes that are considered hazardous to human health.

Correlation between stable nitrogen isotope ratios and concentrations of organochlorines in biota from a freshwater food web.

The relationship between total concentrations of hexachlorocyclohexane (sigma HCH), sigma DDT, and chlorinated bornanes (toxaphene, sigma CHB) and the trophic position of biota from a subarctic lake was investigated using stable isotope ratios of nitrogen (15N/14N). Zooplankton, benthic invertebrates, and forage and piscivorous fishes were analysed for 15N/14N and organochlorines using mass spectrometry and high resolution capillary gas chromatography (GC-ECD), respectively. The trophic relationships of the biota were clearly defined, with 15N/14N increasing an average of 3.3/1000 from prey species to predator. Mean concentrations of sigma HCH were lowest in chironomids (subfamily Chironominae, 0.2 ng/g wet wt.) and highest in burbot liver (Lota lota; 30.2 ng/g wet wt.). Mean concentrations of sigma DDT and sigma CHB ranges from 0.5 and 2.0 (ng/g wet wt.), respectively, in snails (Family Limnaeidae), to 3430 and 2820 (ng/g wet wt.) in burbot liver. Regression analyses indicated that both the wet and lipid weight concentrations of sigma HCH, sigma DDT, and sigma CHB in the biota from this food web were significantly related to trophic position, as defined by delta 15 N. Results from this study indicated that delta 15 N can be used to predict concentrations of organochlorines in freshwater biota.

Whole lake addition of cadmium-109: radiotracer accumulation in the mussel population in the first season.

Cadmium with the radiotracer 109Cd was added to the epilimnion of Precambrian Shield Lake 382 in the Experimental Lakes Area, northwestern Ontario to monitor pathways of Cd from water to abiotic and biotic components, to quantify Cd accumulation and distribution in biota and to evaluate adverse biological and ecological effects. This experiment will permit evaluation of the adequacy of the water quality guidelines of 0.2 microgram Cd l-1 in protecting aquatic life in softwater lakes. As part of the whole-lake experiment, we monitored the activities of 109Cd in various body parts of the floater mussel Anodonta grandis grandis to determine accumulation and distribution of Cd. Additions of Cd from 23 June to the end of October 1987 (a total of 900 g Cd and 89 mCi of 109Cd) increased the total [Cd] in the water from 1.6 to about 85 ng l-1. Cadmium-109 was accumulated in body parts of the mussels, in increasing concentration: mantle less than foot less than gill less than visceral mass less than kidney. After 4 months exposure to the increased water [Cd], the mussels had increased body burden of Cd by an estimated 5-9 times. At the latter increase, the population of 7330 +/- 2100 mussels in the lake contained an estimated 0.011-0.020% of the added 109Cd.

Losses of biota from American aquatic communities due to acid rain.

Models based on chemical survey data and geochemical assumptions were calibrated for areas where rates of acidification are known, then used to predict the declines in alkalinity and pH of lakes in the eastern and midwestern U.S.A. These results were combined with known acid tolerances of different taxonomic groups to estimate the extent of damage caused by acid rain to biological assemblages.An average of over 50% of the species in some taxonomic groups have probably been eliminated from lakes in the Adirondacks, Poconos-Catskills and southern New England. Moderate damage to biotic communities was predicted for lakes in central New England, and north-central Wisconsin. Damage predicted in Maine, upper Michigan, northeastern Minnesota and the remainder of the upper Great Lakes region was slight. Crustaceans, molluscs, leeches and insects were among the most severely affected groups. Among fishes, species of minnows (Cyprindae) were depleted in the most heavily acidified regions, with some declines in salmonid and centrarchid species.Predicted damage to individual lakes in all areas was highly variable. In areas receiving highly acidic deposition, 100% of the species in acid-sensitive taxonomic groups were eliminated in some lakes, while damage to other lakes was predicted to be slight.Estimated damage varied from lake to lake within each subregion, based on chemical characteristics. The most heavily damaged lakes in the Adirondacks and Pocono-Catskills have probably lost all species of molluscs, leeches and crustaceans. On the other hand, lakes of the Midwest showed either slight increases or decreases in the richness of predicted biotic communities.The possible ranges of original sulfate concentrations in lakes and the proportion of sulfuric acid in precipitation that liberated base cations from catchments were confined to relatively narrow limits by the model.

Fates of metal radiotracers added to a whole lake: accumulation in slimy sculpin (Cottus cognatus) and white sucker (Catostomus commersoni).

Six gamma-emitting isotopes, iron-59, cobalt-60, zinc-65, selenium-75, cesium-134 and mercury-203, were added in mid-summer to Lake 224 of the Experimental Lakes Area in northwestern Ontario, Canada. Isotope activities in whole bodies of slimy sculpins and in blood, gills, gut contents, kidney, liver and spleen of white suckers were determined for periods up to 247 days after isotope addition. Results demonstrate delay between contamination of a lake and transfer of contaminant to these fish species. General relationships between movement and distribution of isotopes in water and their accumulation in these fish indicate that direct accumulation from water is not a major route of uptake.