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f <br /> 190 <br /> 5. POTENTIAL FOR HUMAN EXPOSURE <br /> Plants and animals may bioconcentrate lead but biomagnification has not been detected. In general, the <br /> highest lead concentrations are found in aquatic and terrestrial organisms that live near lead mining, event <br /> smelting, and refining facilities; storage battery recycling plants; areas affected by high automobile and truck react <br /> traffic; sewage sludge and spoil disposal areas; sites where dredging has occurred; areas of heavy hunting when <br /> (lead source from spent shot); and in urban and industrialized areas. Lead may be present on plant have <br /> surfaces as a result of atmospheric deposition, whereas its presence in internal plant tissues indicates entire <br /> biological uptake from the soil and leaf surfaces. Although the bioavailability of lead in soil to plants is of thi <br /> limited because of the strong absorption of lead to soil organic matter, the bioavailability increases as the probf <br /> pH and the organic matter content of the soil are reduced. Lead is not biomagnified in aquatic or signif <br /> terrestrial food chains. It may contaminate terrestrial plants as a result of atmospheric deposition and partic <br /> uptake from soil, and animals as a result of inhalation of contaminated ambient air or ingestion of <br /> contaminated plants. Older organisms tend to contain the greatest body burdens of lead. In aquatic 5.3.2. <br /> organisms, lead concentrations are usually highest in benthic organisms and algae, and lowest in upper <br /> trophic level predators (e.g., carnivorous fish). High bioconcentration factors (BCFs) were determined in The c <br /> studies using oysters (6,600 for Crassostrea virt?inica), freshwater algae (92,000 for Senenastrum fou <br /> capricornutum) and rainbow trout (726 for Salmo gairdneri), although most median BCF values for aquatic found <br /> biota are significantly lower: 42 for fish, 536 for oysters, 500 for insects, 725 for algae, and 2,570 for salt c <br /> mussels (Eisler 1988). Ls <br /> Lead is toxic to all aquatic biota and organisms higher on the food chain may table <br /> experience lead poisoning as a result of eating lead-contaminated food. Organolead compounds, such as stable <br /> trialkvI and tetraalkyl lead compounds, are more toxic than inorganic forms and have been shown to co <br /> hioconcentrate in aquatic organisms. Biomagnification of organolead compounds has not been shown and volsoluutioti( <br /> depuration is relatively rapid, with half-life values of 30-45 hours for rainbow trout exposed to tetramethyl and <br /> i l <br /> a <br /> lead. Tetraalkyl lead compounds are more toxic than trialkyl lead compounds, and ethyl forms are more and n <br /> toxic than methyl forms (Eisler 1988). the se <br /> impor <br /> 5.3.2 Transformation and Degradation <br /> In wai <br /> 5.3.2.1 Air compo <br /> lead. <br /> Information available regarding the chemistry of lead in air is limited. Lead particles are emitted to the more <br /> atmosphere from automobiles as lead halides (mostly PbBrCI) and as double salts with ammonium halides lead. <br /> (e.g., 2PbBrCI•NH aCI, Pb31P0412, and PbSOa [Biggins and Harrison 1979; Ter Haar and Bayard 1971�)' Remoi <br /> After IS hours, approximately 75% of the bromine and 30-40%- of the chlorine disappear with lead days (] <br /> carbonates, oxycarbonates and oxides produced. These lead oxides are subject to further weathering to <br /> form increased carbonates and sulfates (Olson and Skogerboe 1975). Lead particles are emitted from mines 5.3.2.: <br /> and smelters primarily in the form of the lead-sulfur compounds, PbSO4, PbO*PbSOa, and PbS (EPA 'There <br /> 1986a). In the atmosphere, lead exists primarily in the form of PbSO4 and PbCOT It is not completely <br /> clear how the chemical composition of lead changes during dispersion (EPA 1986a). Monitoring studies sulfate <br /> indicate that tetraalkyl lead, present in both urban and rural air, may react with hydroxyl ions to form ionic returne <br /> trialkyl and dialkyl species that are more stable in the atmosphere. Relatively recent lead exposure will <br /> be by oxides, whereas aged lead surfaces most likely contain carbonates and basic carbonates. Urban air Limiter <br /> in England that is adverted to rural areas may contain up to 5% of the total lead as alkyl lead; this to soil. <br /> percentage may increase to 20%. for maritime air, with trialkyl lead being the predominant species (Hewitt highly <br /> and Harrison 1987). <br /> s <br /> Based on the vapor pressure of tetraethyl lead (0.26 mm Hg at 20°C) and tetramethyl lead (26.0 mm Hg <br /> at 200C), these two compounds exist almost entirely in the vapor phase in the atmosphere (Eisenreich et <br /> al. 1981). When exposed to sunlight, they decompose rapidly to trialkyl and dialkyl lead compounds and <br /> °i <br />