Tim Wall, Discovery News, 4 Oct 13;
High levels of methylmercury are known to accumulate in the fatty tissues of large ocean-going fish such as tuna, swordfish and marlins. Though most people do not eat enough of these types of fish to result in mercury poisoning, pregnant women are advised to restrict their intake because of the risk to the fetus.
Now it looks like climate change may make the consumption risk even greater.
Biologists observed higher accumulation of methylmercury in killifish, a small fish, as temperatures increased both in the wilderness of Maine and in laboratories.
The contamination levels in the fish may increase with temperature because the metabolism of the tiny fish speeds up in warmer water, according to the recent research published in PLOS ONE. The cold-blooded fish eat more and thereby pick up more methylmercury from the environment.
Coal-burning power plants produce most of the mercury pollution in the atmosphere. When the mercury falls back to Earth’s surface it lands either in the ocean or on land where it can be washed into lakes, streams, and eventually the ocean. Certain bacteria transform the mercury into methylmercury, a more toxic form. After this bacterial conversion, the methylmercury enters the food chain, accumulating in fatty tissues. When people worry about mercury in their fish and other seafood, it is actually this bacterially-altered form of methylmercury.
In the lab, the biologists conducting the study replicated the increasing temperatures likely to occur as climate change continues. The highest levels of mercury contamination occurred in the fish in the warmest water (27 degrees Celsius or 80°F). They also fed the fish mercury-enriched food. “The fish in warmer waters ate more but grew less and had higher methylmercury levels in their tissues,” the authors reported in a press release.
In nature, killifish from different salt marsh pools on the coast near Wells, Maine, served to also replicate the effects of varying degrees of temperatures. The water in some pools reached higher temperatures than others, ranging from 18 to 22 degrees Celsius (65°F to 72°F). Once again, the warmer pools held fish with greater levels of mercury, even though they were only feeding on insects, worms and other natural food sources.
Many larger fish feed on the killifish, varieties of which live around the globe. Mercury in the smaller fish transfers to the larger fish. Mercury continues to build up in the food web, until it reaches the top predator on the planet, us.
Warmer oceans could raise mercury levels in fish
Phys.org, 3 Oct 13;
Oct. 3, 2013 — Rising ocean surface temperatures caused by climate change could make fish accumulate more mercury, increasing the health risk to people who eat seafood, Dartmouth researchers and their colleagues report in a study in the journal PLOS ONE.
Until now, little has been known about how global warming may affect mercury bioaccumulation in marine life, and no previous study has demonstrated the effects using fish in both laboratory and field experiments. Mercury released into the air through industrial pollution can accumulate in streams and oceans and is turned into methylmercury in the water.
The researchers studied killifish under varying temperatures in the lab and in salt marsh pools in Maine. Fish in the marshes ate insects, worms and other natural food sources, while the lab fish were fed mercury-enriched food. Results showed the fish in warmer waters ate more but grew less and had higher methylmercury levels in their tissues, suggesting increases in their metabolic rate caused the increased uptake of the toxic metal.
Experimental and Natural Warming Elevates Mercury Concentrations in Estuarine Fish
Jennifer A. Dijkstra, Kate L. Buckman, Darren Ward, David W. Evans, Michele Dionne, Celia Y. Chen
PLOS ONE, 12 Mar 13;
Abstract: Marine food webs are the most important link between the global contaminant, methylmercury (MeHg), and human exposure through consumption of seafood. Warming temperatures may increase human exposure to MeHg, a potent neurotoxin, by increasing MeHg production as well as bioaccumulation and trophic transfer through marine food webs. Studies of the effects of temperature on MeHg bioaccumulation are rare and no study has specifically related temperature to MeHg fate by linking laboratory experiments with natural field manipulations in coastal ecosystems. We performed laboratory and field experiments on MeHg accumulation under varying temperature regimes using the killifish, Fundulus heteroclitus. Temperature treatments were established in salt pools on a coastal salt marsh using a natural temperature gradient where killifish fed on natural food sources. Temperatures were manipulated across a wider range in laboratory experiments with killifish exposed to MeHg enriched food. In both laboratory microcosms and field mesocosms, MeHg concentrations in killifish significantly increased at elevated temperatures. Moreover, in field experiments, other ancillary variables (salinity, MeHg in sediment, etc.) did not relate to MeHg bioaccumulation. Modeling of laboratory experimental results suggested increases in metabolic rate as a driving factor. The elevated temperatures we tested are consistent with predicted trends in climate warming, and indicate that in the absence of confounding factors, warmer sea surface temperatures could result in greater in bioaccumulation of MeHg in fish, and consequently, increased human exposure.
