A comprehensive study on the ecological toxicity and risk of triphenyltin to aquatic organisms

Abstract

Since the 1960s, contamination of coastal waters by triphenyltin compounds (TPTs) has become a worldwide problem, which is due to their intensive use as effective biocides for diverse industrial and agricultural purposes. However, the chronic toxicities of TPTs and their toxic mechanisms in marine organisms are still poorly known. Although the combined toxicities of different organotin compounds, such as TPT and tributyltin (TBT), are thought to be additive, there is a lack of scientific evidence to support this postulation. TPTs are commonly applied with copper (Cu) in antifouling paints and thus they often co-exist in the marine environment. Yet, their interacting effects on marine biota remain unknown. This study, therefore, aimed to address these knowledge gaps by investigating the toxicities of TPT and its mixtures with TBT or Cu to various marine organisms.

The toxic mechanism of TPT in the diatom Thalassiosira pseudonana was revealed by studying its growth, photosynthesis and molecular responses (i.e., proteome and gene expression) towards TPT exposure. Defensive mechanisms were induced when the diatom was exposed to relatively low TPT concentrations (0.5 μg/L), but high concentrations of TPT (≥ 1.0 μg/L) suppressed the expression of various essential proteins and hence inhibited the growth and photosynthesis of the diatom.

In the rotifer Brachionus koreanus, a significant reduction in the population growth rate was found at ≥3.0 μg/L TPT. Among 12 studied genes, hsp90α2, GST-O and CYP3045C1 genes were significantly up-regulated in the rotifer, possibly as ways to offer cellular protection against the TPT-mediated oxidative stress and facilitate detoxification of TPT. In the marine copepod Tigriopus japonicus, a male-biased sex ratio were found in the second generation after exposure to waterborne TPTCl (≥0.5 μg/L), and a population extinction could occur at 1.6 μg/L TPTCl. Gene expression profiles also indicated that TPT may cause dysfunction of detoxification systems and affect the moulting process in T. japonicus.

In the marine medaka Oryzias melastigma, a life-cycle chronic exposure to TPT led to a significant reduction in body length and retardation of swimming activity of the fish larvae at day 1 of post-hatching. At TPT concentration as low as 0.1 μg/L, the fish population displayed a male-biased sex ratio with a smaller gonadosomatic index in females, which could ultimately cause a population decline.

The interactive effects of both TPT-Cu and TPT-TBT mixtures were modeled as antagonistic according to the concentration additive response surface model, whereas the interactions were suggested to be species specific with a tendency of having synergistic effects based on the response additive response surface model. Apparently, the combined effects of these mixtures are very complex and highly species-dependent, rather than simply follow the concentration addition as predicted.

Finally, a chronic predicted no-effect concentration for TPT was estimated at 0.31 ng Sn/L which is lower than its ambient concentrations in some coastal environments of the world. This study evidently demonstrated that TPT is highly toxic to a variety of marine organisms even at environmentally relevant concentrations. Therefore, TPT compounds should be treated as priority chemicals for tightened regulation and environmental surveillance.