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Sediment recognized as a potential risk 899 cases

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Unformatted text preview: gulated and the release of mercury reduced in 1970. FACTORY some methylation SEA WATER MARINE ORGANISMS SEDIMENTS more methylation RESUSPENSION SOME ANIMALS HUMANS EXPORT Figure 31 The movement and environmental methylation of mercury in Minamata Bay The organometallic compound, methyl mercury was the major cause of the disease. Met hyl mercury is lipid soluble and tends to bioaccumulate in organisms as well as through the food chain ( see Chapter 1, Section 1.3.3, for more information on KOW). Although some methyl mercury was produced in the factory, more was synthesized through the activity of microorganisms in the sediments of Minamata Bay (Figure 3-26). Similar poisonings have occurred in Canada and other locations from mercury released from chlorine production facilities. Spectacular human poisonings have also occurred in other parts of the world, mainly as a result of the mistaken consumption of organo -mercury treated grain intended for use as treated seed. 3.3.5 Substances affecting the endocrine system. Effects of anthropogenic substances on wildlife were first brought to the attention of the public through the publication of Rachel Carson‘s ―Silent Spring‖ in 1962 (Carson 1962). Since the publication of ―Silent Spring‖, our understanding of the fate, behavior, and effects of substances in the environment has advanced considerably. Regulatory action has been taken against many of the substances that caused adverse effects in wildlife. However, like the peeling of an onion, the results of regulatory action to cure one problem may reveal another that was hidden before. This has been the case with the endocrine modulating substances and their effects in wildlife and humans. Although many substances were known to exert their ef fects in humans and other organisms via the endocrine system, the possibility that these substances were causing adverse effects in the environment was not brought to the attention of the public until the publication of ―Our Stolen Future‖ (Colborn et al. 1996). One of the important considerations in assessing these effects in wildlife was that the causative agents were persistent, bioaccumulating, and toxic substances (The PBTs). These substances possessed both great persisten ce and great lipid solubility, the combination of which lead to large concentrations accumulating in organisms at the top of the food chain. Thus, fish -eating birds (and other organisms of similar feeding habits) were not only exposed to greater doses tha t other organisms lower on the food chain but were exposed throughout their life -cycle. These continuous exposures are important because they can interact with annual or seasonal periods of greater sensitivity, such as those related to reproductive activi ty. Thus, as organisms pass through stages of sensitivity under conditions of continuous exposure, the effects of the endocrine modulating substances can be expressed at maximal intensity ( Figure 3-27). The converse of this is that organisms may be very insensitive to endocrine modulating substances at other times. This is very important as, in effect, i...
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