When people hear about ocean pollution, they think, first and foremost, about plastic, dump waste from factories, pesticides washed away from the farmlands or petroleum pollution from oil spills and tanker wrecks. Undoubtedly, all the aforementioned issues deserve public and legal attention, but, in fact, the problem of ocean pollution is not limited to those cases. Obviously, mercury pollution is seldom recalled among the ocean problems. Many people do not even know about this issue and its magnitude, not to mention the channels of pollution and major pollutants. Nevertheless, mercury pollution is the ubiquitous, multi-faceted, worldwide problem of the ocean and coastal waters (Sources to seafood, 2012).
Despite the global effort to reduce the amounts of mercury input and successful implementation of these policies in some countries, the quantity of mercury annually released to the environment from human activities is still on the rise (Sources to seafood, 2012). Mercury is a naturally occurring toxic heavy metal that in concentrations exceeding the norm negatively affects the functioning and development of the central nervous system in wildlife. Moreover, it is prone to accumulate in tissues and being transferred through generations from mothers to offspring during pregnancy and lactation (Schweiger, Stadler & Bowes, 2006).
The sources of mercury pollution are numerous. According to The Coastal and Marine Mercury Ecosystem Research Collaborative (C-MERC) classification, marine waters can be schematically divided into four types of mercury systems based on the input source. The first type referred to as “open ocean systems” get about ninety percent of mercury concentration from atmospheric deposition. Since mercury is not a regular constitute of the atmospheric composition, a reasonable question may arise on how mercury gets into the atmosphere, in the first place. It appears that mercury is emitted into the air from natural sources (for example, volcanoes), anthropogenic sources (such as fossil fuel combustion and mining) and previously deposited mercury originating from both nature and anthropogenic factor. The second type of water systems is the so-called “ocean current systems” that receive the most of toxic loading from mercury that gulfs receive from ocean currents. Finally, nearshore coastal waters labeled as “watershed systems” and “mixed input systems”, receive mercury from rivers, in addition to a direct exposure to mercury concentrated in the atmosphere. The rivers receive their “dose” of mercury in the watershed upstream and carry it downstream to estuaries and bays. The particular sources of mercury input into the environment include inter alia, former gold mines, wastewater treatment plants, waste incinerators, cement plants and chlor-alkali plants. Among the aforementioned, one polluter has caught a special attention of several recent studies (Sources to seafood, 2012; Schweiger, Stadler & Bowes, 2006; Main, 2013).
The studies have found small-scale or “artisanal” mining to be the main source of mercury pollution. Because of mercury’s ability to bind with precious metals, mankind has used it for thousands of years for mining gold and silver. Consequently, one the one hand, mercury is released into the atmosphere during the process of gold isolation from the rock into which it is embedded. On the other hand, it is also dissolved in water used in the process of precious metal extraction as well as in rainwater that runs through the byproducts of mining and then falls into rivers and, consequently, oceans. A great number of such mines function illegally in developing countries such as Peru. However, developing countries are not the sole sources of mercury pollution. According to the 2006 estimates, the United States alone released over a hundred tons of mercury pollution into the atmosphere that penetrated into lakes, rivers and oceans. In fact, this trend persists on an annual basis and on the global scale. Thus, as clearly seen, mankind is the major contributor of mercury into the environment, both directly into the waters as well as into the atmosphere in the form of emissions (Sources to seafood, 2012; Schweiger, Stadler & Bowes, 2006; Main, 2013; Woods Hole Oceanographic Institution, 2007; Mercury contamination, n.d.).
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The first frontier of mercury victims is wildlife. Sadly, the negative impacts of mercury on wildlife are unknown to the vast majority of people and are seldom illuminated in news reports or in other popular media. Remaining unnoticed and unprotected from mercury exposure and its dangerous/deadly concentrations in ocean waters, wildlife species are constantly accumulating mercury in their bodies at levels threatening their health and lives. Perhaps, the most well-documented effect of mercury pollution on wildlife is in fish. Such narrow focus of interest and awareness can be explained by concerns about implications for the human health from consuming these fish species. Humans’ exposure to mercury, especially to its harmful levels and for a prolonged time, may result in developmental and other neurological problems in children and cardiovascular diseases in adults (Schweiger, Stadler & Bowes, 2006; Mercury contamination, n.d.). In addition to circulating in the food chain, mercury’s presence in the environment is a vicious circle. It is emitted and re-emitted from the water and soil into the air, and vice versa. Being a volatile element, mercury evaporates at low temperatures of the natural environment, contaminates the atmosphere and then can be deposited back to the ground and water. The saddest part about dealing with mercury is its ability to accumulate and persist through centuries. The most of the amount of mercury that enters the ocean after falling from the atmosphere or being washed by rivers is the so-called “legacy” mercury that is already present in the environment from past centuries of human activities (Main, 2013; Woods Hole Oceanographic Institution, 2007).
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