RESUMEN
Chemical pollution is one of the major threats to global freshwater biodiversity and will be exacerbated through changes in temperature and rainfall patterns, acid-base chemistry, and reduced freshwater availability due to climate change. In this review we show how physico-chemical features of natural fresh waters, including pH, temperature, oxygen, carbon dioxide, divalent cations, anions, carbonate alkalinity, salinity and dissolved organic matter, can affect the environmental risk to aquatic wildlife of pollutant chemicals. We evidence how these features of freshwater physico-chemistry directly and/or indirectly affect the solubility, speciation, bioavailability and uptake of chemicals [including via alterations in the trans-epithelial electric potential (TEP) across the gills or skin] as well as the internal physiology/biochemistry of the organisms, and hence ultimately toxicity. We also show how toxicity can vary with species and ontogeny. We use a new database of global freshwater chemistry (GLORICH) to demonstrate the huge variability (often >1000-fold) for these physico-chemical variables in natural fresh waters, and hence their importance to ecotoxicology. We emphasise that a better understanding of chemical toxicity and more accurate environmental risk assessment requires greater consideration of the natural water physico-chemistry in which the organisms we seek to protect live.
Asunto(s)
Animales Salvajes , Contaminantes Químicos del Agua , Animales , Organismos Acuáticos , Agua Dulce , Branquias , Contaminantes Químicos del Agua/toxicidadRESUMEN
Many fish populations are exposed to harmful levels of chemical pollution and selection pressures associated with these exposures have led to the evolution of tolerance. Our understanding of the physiological basis for these adaptations is limited, but they are likely to include processes involved with the absorption, distribution, metabolism and/or excretion of the target chemical. Other potential adaptive mechanisms include enhancements in antioxidant responses, an increased capacity for DNA and/or tissue repair and alterations to the life cycle of fish that enable earlier reproduction. Analysis of single-nucleotide polymorphism frequencies has shown that tolerance to hydrocarbon pollutants in both marine and estuarine fish species involves alteration in the expression of the xenobiotic metabolism enzyme CYP1A. In this review, we present novel data showing also that variants of the CYP1A gene have been under selection in guppies living in Trinidadian rivers heavily polluted with crude oil. Potential costs associated with these adaptations could reduce fitness in unpolluted water conditions. Integrating knowledge of local adaptation to pollution is an important future consideration in conservation practices such as for successful restocking, and improving connectivity within river systems.This article is part of the themed issue 'Human influences on evolution, and the ecological and societal consequences'.