Coupling marine monitoring and risk assessment by integrating exposure, bioaccumulation and effect studies : a case study using the contamination of organotin compounds in the Danish marine environment

Abstract

This Ph.D. thesis focuses on the highly toxic organotin compounds, mainly tri-n-butyltin (TBT) but also triphenyltin (TPhT), which have been widely used as antifouling agents in ship paints, and covers several aspects investigated by field studies of spatial distributions, bioaccumulation and ecotoxicological effects in Danish and Greenlandic waters. The amount of field data (from own, national and regional studies and surveys) presented in this thesis has provided an opportunity to integrate actual measured concentrations of contaminants with biological effect studies in a case study that couples marine monitoring and risk assessment for the organotin compounds. Thereby the thesis may also be seen as model for integrated risk assessment of other hazardous substances. The studies presented in this thesis include analyses of organotin in sediments and marine organisms at various trophic levels to assess the distribution and contamination levels in the Danish and Greenlandic marine environment. The various studies show that in general high levels of organotin contamination occur in the Danish waters. Organotin, especially butyltin compounds, can be detected in all regions in a concentration range, which covers five to six orders of magnitude, from contaminated harbour areas and into coastal waters and the sublittoral parts of the open waters. However, the choice of suitable matrices and bioindicators is important for such a wide-range assessment, because of a high variation in accumulation potential of organotin between different species even at the same trophic level of the food web. In Danish coastal waters TBT and breakdown products were found in all trophic levels of the marine food web, from seaweed and invertebrates to fish, birds and marine mammals. The highest butyltin levels, which can reach several µg/g ww, are found to accumulate in liver of harbour porpoise, although comparable levels can also be found in molluscs and fish sampled inside contaminated harbour areas. These studies are supported by biomarker studies of endocrine disruptions in prosobranch gastropods, e.g. imposex and intersex, which specifically can be related to exposure to TBT or TPhT. In addition, a discussion of the risks posed by organotin to organisms at higher trophic levels is included. For instance, marine mammals such as the harbour porpoise may be at risk due to a relatively high intake and accumulation of these substances. But because of the nature of field studies where the influence of confounding factors is difficult to assess, only indications of impairment are provided. The use of biological effect parameters, which can not specifically be linked to exposure to a single type of contaminants, or cause, is also discussed in relation to a study, which examined the impact on larval development in a viviparous fish, the eelpout, in Danish coastal waters. In addition, some other studies of contaminant-induced biological effects, which not specifically can be related to organotin exposure, will also slightly be touched on. Finally an approach to derive a five-class scheme of assessment criteria of TBT is developed. The assessment criteria have been derived to reflect in the objectives within the OSPAR and EU strategies for priority substances for protection of the marine ecosystems in transitional and open waters. In the development of the five status classes it has been possible to combine the TBT concentration in three matrices, e.g. in seawater, sediment and the bivalve M. edulis, with the TBT-specific biomarker responses, e.g. imposex and intersex in five species of prosobranch gastropods. The main advantages with this combined scheme of assessment criteria are that monitoring of TBT levels and TBT-specific biomarker responses can supplement each other in a comprehensive evaluation of the environmental quality in the marine environment over a large scale, both with respect to location and level of TBT contamination. Various kinds of available monitoring and other field data of TBT concentrations and effects can thereby be integrated in the assessment of the TBT contamination in the Danish and neighbouring waters.