Experimental Studies of Chronic Toxicity of Tributyltin Compounds

Abstract

This chapter examines chronic toxicity of TBT through a discussion of five comprehensive studies performed during the last 8 y. The studies share the following characteristics. They are experimental studies conducted under laboratory conditions and designed to demonstrate a causal relationship between TBT exposure and a sublethal response, which was usually reduction in growth or abnormal development; Biol.ogical endpoints, such as metamorphosis or hatching, usually defined the period of observation; and experiments lasted more than 96 h in all cases. The studies are characterized as a progression of exposure levels that began above 1 µg l^-1, but dropped to 1–10 ng l^-1, concomitant with increasingly sensitive chemical analysis methods for TBT. The lowest levels tested are similar to those found in many nearshore and estuarine habitats. Test organisms include developmental stages of fish (Leuresthes tenuis), decapod crustaceans (Rhithropanopeus harrisii), mysid shrimp (Acanthomysis sculpta), oysters (Crassostrea gigas), and clams (Mercenaria mercenaria). Results of these studies demonstrate a range of taxonomically correlated sensitivity to TBT of two to three orders of magnitude. Fish and crab larvae were most tolerant, with exposures in excess of 1 µg l^-1 causing notable reductions in growth or survival. Mysids formed an intermediate group, with a sensitivity about one order of magnitude less. Clams and oysters are the most sensitive group, showing significant sublethal effects in TBT concentrations of 10–50 ng l^-1. The taxonomic pattern of sensitivity depends, at least partially, on possession of metabolic pathways to rid tissue of TBT. Studies with molluscs clearly show a ca usal relationship between TBT exposure and adverse sublethal effects that is consistent with observations made in field studies.