Report No FR/D0016
Prediction of Effects of Organic Contaminants on
The DOE seeks to improve the scope of environmental monitoring
programmes using marine animals by including an assessment of the impact of pesticides on
marine water quality. Mussels have been used successfully to assess the bioaccumulation
and toxic effects of organic chemicals of urban and industrial origin, but the effects of
pesticides on the physiological parameters measured in these surveys are unknown. It is
essential to establish whether mussels are as sensitive to pesticides as other estuarine
and marine species that the Department may wish to protect through the establishment of
appropriate environmental quality standards. The programme objectives were as follows:
- To quantify the sublethal physiological responses of mussels to bioaccumulation of
environmentally important pesticides.
- To explain these responses in terms of anticipated modes of toxic action.
- To apply quantitative structure-activity relationship (QSAR) modelling to facilitate
extrapolation of conclusions to untested compounds of similar type.
- To test whether there are interactions between the toxicity of representative pesticides
and common environmental contaminants such as hydrocarbons.
- To use the data to interpret results of field studies using mussels.
The work was carried out in the laboratory by exposing mussels to
solutions of pesticides in seawater for periods of up to 7 days, and measuring the effect
on feeding rate, respiration rate and absorption efficiency. These parameters are required
for the calculation of the energy balance of the mussels (termed Scope for Growth (SFG)).
SFG is used to compare the health of mussels in field populations. To facilitate
comparison with such field studies, the levels of pesticides accumulated by the mussels in
our laboratory experiments were measured.
3.Results and Conclusions
- All the compounds tested had an effect on feeding rate, which is
quantitatively the most important variable determining SFG. Respiration rate was only
raised by those compounds (the chlorophenols and tributyltin) known to have specific
effects on respiration at the biochemical level. Elevation of whole animal respiration may
have potential as a marker of impact by these classes of compounds. Absorption efficiency
was too insensitive under laboratory conditions to demonstrate any significant changes
with the toxicants studied.
- The physiological effects of the chlorophenols were clearly related to
the structural characteristics of the molecules, so QSARs of predictive value can be
- Although all the neurotic pesticides tested (which included
organochlorines, pyrethroids, a carbamate and an organophosphate) had some effect on
feeding rate, most appeared to be acting only as non-specific narcotics during the
timecourse of our experiments. They were no more toxic to the mussels than typical urban
contaminants like hydrocarbons. Since some pesticides are highly toxic to crustaceans and
fish, physiological energetics studies with mussels cannot be used to assess their impact
on these species. This limitation also applies to water quality assays using larval
molluscs. There is an urgent need to develop in situ and laboratory based bioassays using
neurotoxin sensitive species (eg. Mysid crustaceans). Mussels, however, were sensitive to
the organophosphate pesticide tested, dichlorvos. Further research to exploit the
potential of this observation is recommended.
- The combined toxicity of dichlorvos and the narcotic hydrocarbon
naphthalene is less than additive, so adverse effects are less than might be predicted.
However, the benefit of environmental clean-up of only one constituent of such a mixture
would be less than expected.
- The present toxicological data base cannot explain all of the adverse
effects on mussel health observed in field studies. There is a need to extend the range of
chemicals analysed in monitoring studies and to increase the toxicological data base.
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