Report No DWI0116

PROVISIONAL ENVIRONMENTAL QUALITY STANDARDS FOR

AZINPHOS-METHYL IN WATER DoE 2348-M

DWI0116

Dec 1989

SUMMARY

I OBJECTIVES

To propose provisional environmental quality standards (PEQSs) for azinphos-methyl for the protection of the different uses of water based on readily available information on its environmental fate and ecotoxicity.

II REASONS

The UK has adopted the dual approach for the control of particularly dangerous substances entering the aquatic environment ('The Red List') by applying limit values and environmental quality standards (EQSs). This report is one of a series aimed at proposing provisional environmental quality standards (PEQSs) for those 'Red List' substances for which no EQSs have so far been derived.

III CONCLUSIONS

Azinphos-methyl is a broad spectrum organophosphorus insecticide. Entry into the aquatic environment is likely to be mainly from diffuse inputs. Azinphos-methyl is not very persistent in natural waters, with hydrolysis and photolysis the main degradation processes.

For the protection of freshwater life a PEQS of 10 ng/l is proposed based on applying a safety factor of 10 to the "no effect" concentration of 0.1 µg/l for Daphnia magna (Dortland 1980). The safety factor takes into account that in acute tests other species were more sensitive than Daphnia. The same PEQS is proposed for the protection of marine life as insufficient data are available to derive a separate standard and the available data indicate that fresh and marine species have the same sensitivity to azinphos-methyl. The PEQSs should be expressed as annual average concentrations, because they are based on chronic data, and as "dissolved" azinphos-methyl. As the highest azinphos-methyl levels in the environment are likely to be associated with run-off from treated land, a PEQS of 100 ng/l is also proposed as maximum "dissolved" concentration to protect against these episodic events. This PEQS is based on the 96-hour LC50 to the amphipod, Gammarus lacustris, taking into account the relatively low persistence of az inphos-methyl. Insufficient environmental data are available to verify the proposed standards for the protection of aquatic life.

Using the ADI of 0.0025 mg/kg body weight for azinphos-methyl (WHO/FAO 1974) and allowing that 1% of the ADI may be derived from drinking water, the resulting acceptable concentration in drinking water is 0.75 µg/l for an adult drinking 2 l water per day. This value is greater than the MAC of 0.1 µg/l laid down for individual pesticides in the EC Drinking Water Directive.

The analytical limits of detection for azinphos-methyl which can currently be achieved by the water industry (approximately 50 ng/l in river waters, Standing Committee of Analysts 1988) are inadequate for monitoring the proposed PEQSs in natural waters. It is recommended that for the determination of "dissolved" azinphos-methyl the sample is allowed to stand for at least one hour before analysis and the supernatant is analysed without filtration.

IV RECOMMENDATIONS

The PEQS values proposed should only be regarded as tentative values because, owing to time constraints, some of the papers quoted could not be fully assessed for the preparation of this report. The standards should therefore be reassessed when all information has been examined in detail.

V RESUME OF CONTENTS

This report uses available information on the ecotoxicity and environmental fate of azinphos-methyl to derive PEQSs for the protection of freshwater and marine life and considers likely safe levels for waters used for abstraction to potable supply. Insu fficient data were available to consider other water uses.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.