Report No DWI0120

Jul 1990

To propose provisional environmental quality standards (PEQSs) for endosulfan for the protection of aquatic life based on readily available information on environmental fate and ecotoxicity.

The UK Government has proposed, in the Ministerial Declaration in response to the second Ministerial Conference on the Protection of the North Sea, tighter controls over the most dangerous substances entering the aquatic environment (DoE 1987). In response to this declaration the DoE have published an agreed 'Red List' of 23 substances (DoE 1989a). This report is one of a series proposing PEQSs for 'Red List' substances for which no environmental quality standards have yet been set.

Endosulfan is a broad-spectrum, non-systemic contact and stomach acting insecticide which is very toxic to fish. Endosulfan is an organochlorine compound and the technical product consists of two isomers of similar toxicity to most aquatic organisms. Endosulfan may be oxidised in water and organisms to endosulfan sulphate which is also toxic. Entry into the aquatic environment may occur from diffuse inputs via spray drift and land run-off, or by point discharges. Chemical and biological degradation result in half-lives of about 4 days in waters of pH >7 or greater than 1 week in water of pH <7 with degradation to the comparatively non-toxic endosulfan diol.

For the protection of freshwater life a PEQS of 10 ng/l is proposed based on applying an arbitrary safety factor of 30 to the acute LC₅₀ of 300 ng/l for rainbow trout (Nebeker et al 1983), Table 1. A smaller safety factor of 30 compared to the more usual 100 has been applied as tests have shown that, for fathead minnow, juvenile fish (7 day LC₅₀ of 0.86 pg/l) and early life stages (NOEC of 0.2 pg/l for full lifecycle tests) have similar sensitivities to endosulfan, Macek et al (1976). The standard of 10 ng/l is expressed as annual average concentration and as "total dissolved endosulfan", which is defined as the sum of the concentrations of the two isomers plus the degradation product endosulfan sulphate and is measured after allowing the sample to settle for one hour before analysis of the supernatant. The standard is based on dissolved endosulfan because environmental data and field trials suggest that endosulfan tends to become adsorbed to suspended solids and that in this form it is not readily bioavailable to aquatic organisms and in particular to fish.

In addition to protect against episodic pollution a PEQS of 1 pg/1 for "total dissolved endosulfan" expressed as maximum concentration is also proposed. This is based on applying an arbitrary safety factor of 30 to the short-term LC₅₀ of 31.9 µg/l obtained by Kleiner et al (1984) for fathead minnow. A safety factor of 30 has been selected by applying a factor of 10 to protect against acute effects and an additional factor of 3 to take into account that other species are more sensitive.

Insufficient data are available to set a standard for total (dissolved and adsorbed) endosulfan.

For the protection of marine life a PEQS of 5 ng/l for "total dissolved endosulfan" expressed as annual average concentration is proposed based on the application of a safety factor of about 10 to the acute LC₅₀ of 40 ng/l for the pink shrimp (Schimmel et al 1977). Only a relatively small safety factor has been applied as the chronic and acute toxicities appear to be similar. No maximum PEQS value is proposed for total or "total dissolved endosulfan" for the protection of marine life.

The analytical limits of detection for endosulfan currently achievable within the water industry (~10 ng/l in river waters, Standing Committee of Analysts 1988) are inadequate for monitoring the proposed PEQSs in natural waters.

Allowing that 1% of the acceptable daily intake (ADI) (0.008 mg/kg body weight, WHO 1984) may be derived from drinking water, the resulting maximum acceptable concentration (MAC) in drinking water would be 2.4 pg/l for a 60 kg adult drinking 2 l per day. This value is much greater than the MAC of 0.1 pg/l laid down in the EC Drinking Water Directive for individual pesticides. No "advisory value" is included for endosulfan in the Guidance on Safeguarding the Public Water Supplies (DoE 1989b).

The PEQS values proposed are based on a wide variety of laboratory toxicity data and evidence from field applications and environmental concentrations. However, insufficient information is available on the fate and bioavailability of endosulfan adsorbed on sediment. The PEQSs should therefore be regarded as guideline values which might need revision when additional data become available.

This report uses available information on the ecotoxicity and environmental fate of endosulfan to derive PEQSs for the protection of freshwater and marine life.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.