Mercury released into the air from coal-fired power plants, burning household waste or mining ore deposits can reach soil and water resources where bacterial processes may transform it into organic mercury-methylmercury forms.
Methylmercury travels up the food chain, poisoning fish and wildlife that humans then ingest as well as finding its way into our drinking water sources. Learn how mercury makes its way into our daily lives.
Burning Coal
Burning coal to generate electricity is the main source of mercury pollution in our oceans and lakes, contributing 2,000 tons per year in gaseous form to enter our waters in gas form from coal-fired power plants, eventually finding its way into fish eaten by humans as neurotoxins like methylmercury. WHOI scientists investigate how toxic mercury enters marine ecosystems as well as freshwater lakes and rivers with an emphasis on decreasing human exposure.
Coal-fired power plants release mercury emissions through several means, depending on the type of coal used and its form of combustion. Coal contains small amounts of mercury bonded to sulfides, clay or organic material which during combustion releases it as mercury sulfide gas into the atmosphere along with other pollutants like nitrogen oxides and sulfur dioxide; after being exhaled into the atmosphere it combines with oxygen from air into methylmercury compounds that travel by wind and rain and become contaminants for drinking water sources in other locations where water quality needs protection from contamination by wind or rain.
Mercury can enter lakes and rivers directly from point sources such as paper mills or battery manufacturers; however, most mercury enters freshwater through atmospheric deposition. This process involves the transformation of inorganic mercury into organic forms that combine with carbon found within living organisms to form methylmercury; neurotoxins that bioaccumulate up the food chain.
Mercury found in atmospheric deposits can also be released when engineers flood land to create reservoirs for hydroelectric power generation. A low oxygen environment promotes bacterial growth that quickly converts elemental or inorganic mercury into its organic form – most toxic for human beings.
At sea, methylmercury pollution begins with microscopic plankton that consumes it and then passes up through food chains until reaching catfish who consume it and consume their flesh–possibly reaching levels dangerous for people who eat the fish themselves.
Fish Consumption
Mercury particles enter lakes, rivers and oceans through two sources: direct point sources such as factory waste management systems or battery manufacturers that improperly manage waste; and atmospheric deposition. Of the two approaches, atmospheric deposition accounts for the majority of mercury entering our environment as it drifts over water surfaces – eventually it combines with carbon to form neurotoxic methylmercury that accumulates as it moves up food chains and accumulates further within living organisms.
Mercury that enters the air is taken up by plants and bacteria in waterbodies, where they help transform elemental mercury into methylmercury, more readily absorbed by organic matter. Small fish absorb this methylmercury before it is eaten by larger predators – increasing mercury concentration levels over time and explaining why people who eat lots of seafood may be at greater risk of mercury poisoning than those who do not consume any seafood at all.
As methylmercury builds up in marine ecosystems, its accumulation can dismantle normal ecological processes and spark an algal bloom that reduces oxygen in the water, which in turn threatens aquatic life and may release large amounts of PCBs and DDT into it. Low oxygen conditions also increase exposure of fish to methylmercury toxins which in turn impact human health when eaten as food sources.
Carl Lamborg of WHOI Biogeochemist Carl Lamborg has conducted extensive studies of sediment samples collected from remote lakes far removed from industrial and mining activities and discovered that levels of methylmercury increased dramatically during the Industrial Revolution in these locations. Now, Carl is researching how methylmercury makes its way into seawater and ocean organisms initially, paying particular attention to interactions between positively charged mercury ions and negatively charged sulfides – and cell membranes as a key step in their conversion to toxic methylmercury.
Sediment Deposition
Mercury pollution enters aquatic ecosystems through atmospheric deposition, where airborne mercury particles in gaseous form return to water as rain, snow or other precipitation. Much of the mercury pollution stems from human activities like irresponsible waste management at mining sites, power plants or waste incinerators; its source may even be traced back further than that.
Why does mercury build up only in some lakes and not others? One theory suggests that different rates of deposition of sediment-bound mercury due to natural or human activities vary between lakes, while microbes in their sediment may influence whether or not it becomes methylated. Gustin has conducted extensive research into Mediterranean sea sediments for both elemental and methylmercury deposition; wet deposition from rainfall as well as dry deposition through litterfall/throughfall can contribute significantly towards total ecosystem mercury concentration.
He investigatedd how sediment’s amount of sulfide influences its ability to form sulfur-rich compounds that are converted to methylmercury by microbes in low oxygen zones below water surfaces, finding that its concentration correlated well with levels of methylmercury found within sediment.
His research, funded by STAR grants, has explored how changes to ocean biogeochemistry contribute to an accumulation of methylmercury in some marine ecosystems. He discovered that the rate of removal can depend on various environmental parameters like water body temperature and salinity levels as well as presence or absence of sulfides on seafloor surfaces or availability of organic carbon sources.
He has also conducted extensive analyses on sediment from several coastal lakes to see if his identified chemical fingerprints help explain why some lakes contain elevated mercury concentrations while others don’t. Furthermore, he tracked how mercury increased over time when human industry entered town, only for it to later decrease after industrial activity ended – his work can help us figure out ways to protect both ourselves and the environment by limiting how much mercury we release into the air, oceans, or lakes.
Methylmercury
Mercury can pollute our waters directly when irresponsible paper mills and battery factories release it into lakes or marine habitats, but most mercury found in rivers, lakes and oceans comes from atmospheric deposition; this process sees airborne mercury particles turn back into liquid form through raindrops or fogfall, increasing atmospheric concentration threefold since pre-Industrial times in remote parts of both hemispheres.
Airborne mercury finds its way to low oxygen zones of the ocean where it combines with microorganisms to form methylmercury, an inedible compound with no degradable source. Unfortunately, it quickly accumulates at the base of marine food chains where fish consume it as their prey; ultimately biomagnifying up the food chain until humans consume it too.
Methylmercury can have less serious health effects than elemental mercury, yet is still very hazardous. Exposure to high levels can damage the nervous system and is especially hazardous to children and unborn babies. Long-term exposure to high levels can cause disturbances in vision and hearing as well as tingling fingers and toes and coordination issues; symptoms also include memory loss and learning disabilities – this exposure often passes from mother-to-baby during gestation or through breast milk.
If you want to avoid mercury poisoning, eating fish and shellfish with low levels of the compound is the ideal way to do it; however, that’s not always feasible; one effective solution to reduce mercury contamination in natural waters is building wetlands which trap and absorb mercury before it reaches open waters.
Water quality improvements from wetlands extend far beyond protecting human health; they improve water quality by filtering excess nitrogen and phosphorus out of freshwater streams into the sea, as well as slowing their outflow. Unfortunately, governments and industries tend to overlook building wetlands despite their proven effectiveness at decreasing mercury pollution in ocean currents; scientists estimate that 10 of the world’s largest rivers account for half of all ocean current mercury pollution.