Organochlorine pesticides have been widely used in the past, but aldrin, DDT, dieldrin and endrin have been banned from use as a pesticide in the UK (PSD/HSE 1998). However, the continued persistence and wide distribution of these substances in the marine environment remain a concern. They are List I and Red List (except isodrin) substances. Two other organochlorine pesticides remain in use: lindane and endosulfan.

Aldrin, DDT, dieldrin and endrin, have been widely used and therefore are found widely distributed in the environment.

Concentrations of aldrin, DDT (and its metabolites: pp-TDE and pp-DDE), dieldrin, endrin and isodrin have been measured in water, sediments and biota as part of the National Monitoring Programme at sites in estuaries and coastal waters throughout the UK. DDT compounds and dieldrin were also monitored in estuarine and coastal waters of England and Wales by the NRA. These results are summarised in Appendix D.

Dieldrin and DDT compounds were detected in the flesh of Mytilus edulis at a small number of sites. Dieldrin, endrin and DDT compounds were detected in fish livers. In sediments, dieldrin and DDT compounds were found at estuarine and intermediate sites. The NRA survey found DDT compounds and dieldrin at concentrations greater than 0.1 mg l^-1 in very few (0.1%) of estuarine and coastal water samples. In general, concentrations are very low and in many cases are considered to be close to background.

In general, these compounds have a low water solubilities, high log Kows and log Kocs. They tend to be persistent and sorb strongly to suspended solids and sediments.

An exhaustive literature review on the toxicity of these organochlorine pesticides has not been carried out for the purposes of this profile. The information provided in this section is taken from existing review documents and directed towards particular areas of concern.

In general, these organochlorine pesticides are highly toxic to aquatic organisms but the bans on their use and their fate and behaviour suggest that water column concentrations are of low concern. This is reflected in low observed water column concentrations. EQSs in the water column exist for total DDT, pp-DDT, total 'drins', aldrin, dieldrin, endrin and isodrin. The standstill provision applies for these substances such that concentrations in sediments and/or shellfish and/or fish must not increase significantly with time.

The majority of the remaining environmental burden of these substances appears to be in the sediment and in marine organisms.

In Canada, interim marine sediment quality guidelines (ISQGs) have recently been set for dieldrin, endrin, DDT and its metabolites. ISQGs for these compounds are: 0.71 mg kg^-1 (dry weight) for dieldrin, 2.673 mg kg^-1 (dry weight) for endrin, 1.19 mg kg^-1 (dry weight) for DDT (sum of all isomers), 2.07 mg kg^-1 (dry weight) for DDE (sum of all isomers) and 1.22 mg kg^-1 (dry weight) for DDD (sum of all isomers). The ISQGs represent the lower end of the range of concentrations at which biological effects are occasionally observed on the native fauna of Canada. They represent only an indication of the concentrations that may occasionally cause effects in the UK.

Organochlorine pesticides (dieldrin, DDT and its compounds, aldrin) have been identified as endocrine disrupting substances. The presence of high concentrations of organochlorine pesticides (and PCBs) or their residues in marine mammals have been suggested as the cause of (or contributing towards) pathological changes and reproductive failures in Baltic seals (Helle et al 1976) sealions, seals and beluga whales (Addison 1989); immunity suppression (and hence the possibility of being more susceptible to disease) in harbour porpoises (Kuiken et al 1994) and seals (Reijnders 1986; Swart et al, 1994); changes in the development stability of the Baltic grey seal (Zakharov and Yablokox 1990); and premature pupping in California sea lions (Delong et al 1973).

In general, organochlorine pesticides tend to be highly bioaccumulated by aquatic organisms (with different degrees of biomagnification reported).

Potential effects include:

• toxicity of organochlorine pesticides to aquatic life at concentrations above the appropriate EQS in the water column;
• Accumulation in sediments and a potential hazard to sediment dwelling fauna at concentrations similar to those indicated by Canadian interim marine sediment quality guidelines;
• bioaccumulation in marine organisms and biomagnification in food chains posing a threat to fish, sea birds and Annex II sea mammals;
• endocrine disruption in fish, sea birds and Annex II sea mammals.

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