Organotins and Hydromineral Homeostasis in Aquatic Animals

Enzymes, non-enzymatic proteins and other organic molecules are vital components in living cells. Their respective function depends on specific spatial configurations which are linked to intracellular conditions. Any fluctuation of these conditions, beyond certain threshold values, such as a disruption of ionic regulatory mechanisms, can lead to the destabilisation of a finely balanced intracellular dynamic physiological equilibrium or homeostasis. Hydromineral homeostasis in aquatic organisms is maintained by a complex endocrine controlled array of specialised cross-membrane ion transport systems and the regulation of membrane water permeability. Depending on how aquatic organisms maintain hydromineral homeostasis, they can be roughly divided into two groups: osmoconformers and osmoregulators; the former are mostly invertebrates with high water permeability, the latter include some invertebrates and most fish species, whose permeable external epithelia are usually restricted to the gills. Other important organs involved in hydromineral regulation include the intestine and the various phyla-specific organisational types of renal systems. Environmental concentrations of organotin compounds, such as tributyltin and triphenyltin, have been shown to interfere with the maintenance of hydromineral homeostasis by inhibiting ATPases and affecting membrane permeability for water. The present chapter reviews the impact of organotin exposure on fresh- and seawater organisms of various phyla by examining the histophathological, physiological and molecular interactions of organotin compounds with relevant enzymes, membranes, the endocrine system, and the consequential ramifications for individuals, populations and community structure in aquatic ecosystems.

Keywords: Hydromineral regulation - gills - membranes- osmosis - ionic flux - organotins - ATPase.