Report No FR/D0017

Jan 1995

1. Laboratory experiments have been carried out to evaluate the effects of sediment contamination on marine and estuarine meiobenthic communities at a range of environmentally realistic concentrations. These microcosm experiments have more ecological 're alism' and their results are of greater ecological significance than single species toxicity tests.
   
2. Low levels of contaminants are known to affect the structure of benthic communities but field data are difficult to interpret because they are often a response to a cocktail of contaminants and are also influenced by natural changes in the environment. Using controlled laboratory experiments it is possible to distinguish the effects of different contaminants. For various reasons which include their smaller size, meiobenthic communities can be more easily studied in the laboratory than macrobenthic communities and are being increasingly used for pollution studies.
   
3. This jointly funded DOE and NRA project interfaces with a two-phase MAFF project concerning the field response of meiobenthos to anthropogenic disturbance and the establishment of field survey protocols. The ultimate objective of the two projects is to provide more sensitive methods for assessing the biological effects of low levels of pollutants using meiobenthic communities.
   
4. A simple microcosm design and methodology was developed to determine the effects of experimentally contaminated sediment or natural field sediment from potentially polluted sites on natural meiobenthic communities. Field collected meiobenthic communities in natural sediment were mixed with defaunated test sediment in small (0.57 l) bottles. The meiobenthos and sediment were covered with filtered sea water which was aerated via an aquarium airstone diffuser. The experiments were maintained in the dark at constant temperature for a period of two months. The meiobenthos in the different treatments was then compared to the meiobenthos in control sediments to determine any effects of the contaminant or the field sediment.
   
5. This microcosm system was used to determine the effects of seven contaminants: Cu, Zn, Cd, Pb, TBT, arochlor 1254 and permethrin on estuarine intertidal and sublittoral meiobenthic communities from different sediment types. Each contaminant was dosed at three levels. The highest dose was near the extreme values found in the UK and was chosen to elicit a response from the meiobenthos if any was likely to occur in the field. The meiobenthos were most strongly affected by the Cu, Zn and arochlor 1254; they were affected by the Pb but not in a dose dependant manner; they were affected by the TBT but only at the high dose levels (the community in estuarine mud was not affected at all); they were not affected by the permethrin or Cd treatments. The sensitivity to the different contaminants and the range of doses differed between the communities tested.
   
6. The system was successfully used as a sediment bioassay to validate results from the MAFF project survey of the meiobenthos of the Fal estuary.
   
7. The results from this study need to be generalised by conducting similar studies elsewhere, to see whether repeatable features of community change can be associated with the effects of specific contaminants. The regulatory authorities should explore the use of meiobenthic community microcosm experiments as routine bioassays for sediments and to set stringent environmental quality standards.

Copies of the report are available from FWR, price £25.00, less 20% to FWR Members.