Chapter 14 - Sublethal Toxicity at the Level of Organism

Abstract

Ecologically relevant sublethal effects are those related to the fitness of the individual, i.e., its ability to survive, grow, and reproduce, because these traits affect population size. If sensitive populations decline as a consequence of pollution the community structure may change and the ecosystem functioning be altered. Sublethal endpoints are the first to be targeted in a pollution event since they may be orders of magnitude more sensitive than the LC50. Sublethal toxicity arises when the exposure levels exceed the thresholds of the physiological mechanisms that maintain the basic biological functions, such as homeostasis and compensation. Repairing toxic effects require extra energy expenditure, and thus sublethal toxicity manifests in a decreased energy budget, fecundity, and growth performance. Scope for growth (SFG) is a physiological index that represents the balance in terms of ratios between the energy gains (feeding, assimilation) and loses (excretion, respiration), i.e., the energy available for growth and reproduction. Recording SFG in filter feeders provides an ecologically relevant and sensitive response to chemicals. Endocrine Disrupting Compounds are synthetic chemicals that interfere with the metabolism of hormones or act as their mimics. The organotin biocide and plastic additive tributyl-tin (TBT) inhibits the synthesis of estradiol causing imposed male traits in gastropod females. The effects of TBT on wild populations improved after the ban of this chemical. Xenoestrogens cause vitellogenin synthesis and other female traits in male fish. Behavioral endpoints (swimming activity or swimming speed, avoidance, burrowing activity, changes in taxis, ventilation rates) are the most sensitive responses to pollutants, although their ecological relevance is warranted only if they are related to the individual's biological fitness. Patterns of fish gill ventilation or bivalve shell closure have been used as biomonitors that allow continuous surveillance of water quality.