Environmental concentration/body burden

Bioconcentration, Bio accumulation and Biomagnification. These aspects are determined by the physicochemical properties of a chemical, an organism s ability to excrete the chemical, the organism s lipid content and its trophic level. Bioconcentration relates to the difference between the environmental concentration and that of the body tissues. A high bioconcentration factor (BCF) predisposes to bioaccnmulation. The upper limit of bioaccnmulation is determined by lipid levels in the organism s tissues. Whether the resultant body burden causes biomagnification in the food chain depends upon the metabolic capabilities of the exposed organism. 

Exposure Levels in Environmental Media. Reliable monitoring data for the levels of di- -octylphthalate in contaminated media at hazardous waste sites are needed so that the information obtained on levels of di-ra-octylphthalate in the environment can be used in combination with the known body burden of di-w-octylphthalate to assess the potential risk of adverse health effects in populations living in the vicinity of hazardous waste sites. Di-u-octylphthalate has been detected in ambient air, rain, surface water, groundwater, and sediment. However, as a result of the confusion about the nomenclature for octylphthalate esters, much of the historical monitoring data available actually pertain to the branched isomer, di(2-ethylhexyl)phthalate (Vista Chemical 1992). Therefore, little current information specific to the /1-octyl isomer is available regarding concentrations of the compound in foods, drinking water, and environmental media, particularly with respect to media at hazardous waste sites. The lack of monitoring data precludes the estimation of human exposure via intake of or contact with contaminated media. 

Wu, N., Herrmann, T., et al (2007) Human exposure to PBDEs associations of PBDE body burdens with food consumption and house dust concentrations. Environmental Science and Technology, 41 (5) 1584-1589. 

These characteristics also determine whether or not a chemical bioconcentrates (body burden concentration > environmental concentration due to absorption from skin or respiratory organs) or bioaccumulates (body burden concentration> environmental concentration due to all routes of uptake). Similar to toxicity tests, bioaccumulation tests are laboratory exposures designed to assess the potential for bioaccumulation or bioconcentration for a chemical. 

Against this backdrop, new studies examining human levels of toxic chemicals -so-called body burden - are continually being published. A 2003 study confirmed the presence of 116 industrial chemicals, most of which are toxic in laboratory animals, in the bodies of average Americans (CDC, 2003). A similar study found even more chemicals in the body of nine volunteers of the 167 chemicals measured, 76 cause cancer in humans or animals, 94 are toxic to the brain and nervous system, and 79 cause birth defects or abnormal development (EWG, 2002). The United Kingdom s Royal Commission on Environmental Pollution has recommended that where synthetic chemicals are found in elevated concentrations in biological fluids such as breast milk they should be removed from the market immediately (RCEP, 2003). 

Molar concentrations or dosages provide a more accurate assessment of the toxicity of a particular compound. This relationship will be explored further in our discussion of quantitative structure-activity relationships. Another weakness of the LC50, EC50, and IC50 is that they reflect the environmental concentration of the toxicant over the specified time of the test. Compounds that move into tissues slowly may have a lower toxicity in a 96-h test simply because the concentrations in the tissue have not reached toxic levels within the specified testing time. L. McCarty has written extensively on this topic and suggests that a lethal body burden or some other measurement be used to reflect tissue concentrations. 

When more knowledge is available on internal effect concentrations, bio-mimetic monitoring may be a useful tool to estimate the environmental risk of organisms in the field, and at present can already be used for narcotic effects. Already mixed-function oxygenase system components and antioxidant enzymes are related to contaminant body burdens in marine bivalves in the field [151], which indicates the potential of the use of internal concentrations as parameters for ecotoxicological effects. 

Relatively little is known about environmental concentrations and the fate and behaviour of the oestrogens in the aquatic environment. There appears to be an increasing burden of oestrogens in water bodies owing to the use of the contraceptive pill—up to 15ngl 1 of ethynyloestradiol have been recorded in some UK... 

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