Mercury Levels

Introduction Bioaccumulation of heavy metals in tissues of animals has received considerable attention because of the lethal and sublethal effects of their accumulation. Heavy metals come from industrial sources, storm water runoff, and agricultural runoff, as well as from natural erosion, biogeochemical cycles, and volcanism. They enter the food chain via air, water, soil and biota, accumulating disproportionately at higher levels of the food chain. Mercury is considered one of the most potentially serious pollutants since it has no known biological function in the body of aquatic animals, is highly toxic and, unlike other heavy metals, tends to be accumulated through the food chain. Furthermore, inputs of mercury to the environment include a large anthropogenic component (Ek et al. 2004). Birds are particularly useful as bioindicators of pollution because they are often high in the food chain (Burger et al. 1994). Several physiological and biological processes, such as feeding habits, growth, age, reproduction, moulting, and migration may influence metal concentration and distribution in birds (Kim et al. 2007). The avian mercury concentration gradient is usually at its highest levels in feathers, followed by liver, kidney, heart, and muscle tissues (Burger 1993). Numerous waterfowl species are regarded as convenient bioindicators of environmental heavy metal pollution. They are readily recognizable, show distinct sexual dimorphism, are long-lived, abundant, and have wide geographical ranges: in other words, they meet the requirements of good biomonitors (Kalisinska et al. 2004). Such species include the Common Teal Anas crecca. Several authors have investigated mercury levels in piscivorous birds such as Great Cormorants Phalacrocorax carbo (Houserova et al. 2007), Australasian Gannet Morus serrator (Burger et al. 1994), Black-Headed Gull Larus ridibundus (Lewis & Furness 1991) and tropical terns (Burger & Gochfeld 1991). However, Rothschild & Duffy (2005) reported mercury concentrations in muscle, brain and bone tissues of Common Teal Anas crecca and other Alaskan waterfowl. The mean values for mercury in Alaskan waterfowl were unlikely to cause adverse reproductive or behavioural effects in the birds. The objective of our study was to determine the levels of mercury in liver and kidney of Common Teal taken from Shadegan Marshes, in southwest Iran.