In recent years, emerging contaminants, including pharmaceuticals and personal care products (PPCPs), have received unprecedented attention from the scientific and regulatory communities and media at the global level. These compounds are often referred to as emerging contaminants because of the limited understanding of environmental occurrence, disposition, or fate, and responses of aquatic and terrestrial ecosystems to realistic exposure scenarios. Such limited information, and the presumption that concentrations to which organisms are routinely exposed are relatively small (e.g., <100 p,gkg~ in soil, <1 mgl 1 in water), have generally hindered the development of sediment/soil screening guidelines and ambient water quality criteria in the United States, or similar metrics in other parts of the world.
PPCPs primarily enter surface waters in discharge from municipal wastewater treatment plants (WWTPs) because plant processes do not completely remove them from inflowing waste. However, PPCPs may also enter the environment from terrestrial applications of bioso-lids or wastewater, biosolid-derived products, leachates from landfills, discharges from on-site septic or aerobic treatment systems, aquaculture practices (e.g., net pens), or transport from intensively reared agricultural areas (e.g., confined animal feeding operations) to aquatic systems. Human and veterinary pharmaceuticals are excreted as a combination of metabolites and parent compounds or are directly discarded into wastewater as unused medications. Although many pharmaceuticals are primarily excreted as metabolites, microbial activity in a WWTP may cleave conjugated metabolites, potentially resulting in reactivation to parent compounds prior to discharge to a receiving ecosystem. Mixtures and metabolites present challenges to understanding exposure and effects, as a number of PPCP classes (e.g., antibiotics) also are expected to co-occur in complex mixtures distributed between solid and aqueous components of the environment.
Unlike non-point aquatic pesticide runoff that generally tends to occur over short periods of time following rain events, potentially resulting in acute toxicity to aquatic organisms, lower-level PPCP exposures at environmentally relevant levels over longer time periods may subtly modulate and alter biochemical, physiological, reproductive, and ecological processes. Subsequently, current approaches for assessing risk to ecosystems that rely on short-term toxicity tests may not be appropriate for PPCPs. The continuous release of PPCPs from WWTPs has resulted in use of the term 'pseudopersistent' to describe the environmental fate of these compounds, since rates of effluent introduction often exceed PPCP half-lives in a receiving ecosystem. Thus, PPCPs present unique challenges to scientists, ecosystem managers, and policymakers, and have stimulated the global scientific community to work toward development of new ecological risk assessment and water quality paradigms for these compounds.
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