Persistent organic pollutants

Finally, we turn to organic pollutants as examples of exotic chemicals (i.e. those introduced by human manufacture) impacting on the global environment. Organic pollutants are considered persistent when they have a half-life (i.e. the time taken for their concentration to decrease by 50%) of years to decades in a soil or sediment and of several days in the atmosphere. Organic pollutants persist in the environment if they are of low solubility, low volatility or resistant to degradation (see Section 4.10.1 & Box 4.16). Stable aromatic compounds, and highly chlorinated compounds, for example polychlorinated biphenyls (PCBs), poly-chlorinated dibenzo-p-dioxins and furans (PCDD/Fs), 2,2-bis-(p-chlorophenyl)-1,1,1-trichloroethane (DDT) and hexachlorocyclohexane (HCH) (Fig. 7.25) are good examples. The deleterious health effects of these molecules on humans and other animals are widely documented being potentially carcinogenic (PCBs, PCDD/Fs, DDT, HCHs), mutagenic (PCDD/Fs) and able to disrupt immune, nervous and reproductive systems.

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