Deltamethrin in freshwater and marine water

Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals' of the ANZECC & ARMCANZ (2000) guidelines.

The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.

Description of chemical

Deltamethrin (CAS 52918-63-5 and 52820-00-5) is a synthetic pyrethroid with different chiral forms, produced by Roussel Uclaf. Its IUPAC name is (S)-α-cyano-3-phenoxybenzyl(IR,3R)-3-(2,2-dibromovinyl)-2,2-=dimethylcyclopropanecarboxylate (or IR)-cis-isomer. It has a molecular weight of 505.2 and its formula is C₂₂H₁₉Br₂NO₃. It is almost insoluble in water (<0.2 µg/L at 25°C) and its log K_ow is 4.6 at 25°C (Tomlin 1994). Many other pyrethroids have log K_ow values between 5 and 7 and log K_oc values from 3.5 to 5.5 (Hill et al. 1994).

Uses and environmental fate

Deltamethrin is used against a wide variety of insect and arachnid pests and has over 230 registered uses in Australia (NRA 1997a). It is used on around 25 food crops including cereal, vegetables and is also used on cotton, tobacco and wildflowers. Deltamethrin has extensive household use in food preparation areas, and is also used on animals against external parasites and on timber against borers.

Deltamethrin is more stable in acidic conditions rather than in alkaline (Tomlin 1994). Most pyrethroids adsorb very strongly to suspended matter and biological surfaces within a few hours and are transplanted to bottom sediments with settling. Only extremely low concentrations will remain dissolved in the water column (Hill et al. 1994). Pond studies have confirmed that this trend applies to deltamethrin (Maguire et al. 1989, Muir et al. 1992). Adsorption to plants and loss from surface films by evaporation can also increase the rate of loss of pyrethroids. Surface films may increase exposure for some surface-feeding species, such as some cladocerans.

Aquatic toxicology

Freshwater fish: two species, 48 to 96-hour LC50, 0.5 to 3.5 µg/L. An additional species Tilapia nilotica had a 96-hour LC50 of 15 µg/L but this was well above water solubility.

Freshwater crustaceans: one species, 48 to 96-hour LC50 or EC50 (immobilisation), 0.003 to 1.010 µg/L. The lowest figure of 0.003 µg/L was almost an order of magnitude lower than the next figure (0.01 µg/L), for the same species, Daphnia magna.

Freshwater insects: one species, 96-hour LC50, 0.15 µg/L. Data from another eight species did not meet screening criteria.

Freshwater mussel: two species, 96-hour LC50, 22,000 to 410,000 µg/L, well above water solubility.

Freshwater mesocosms: A number of pyrethroids have been tested in field systems and given that exposures for different pyrethroids are similar, depending on physico-chemical properties, there is a strong concurrence of biological observations (Hill et al. 1994). Reported mesocosm experiments with deltamethrin did not meet the requirements for use in guideline derivation due to insufficient treatments or replicates (e.g. Cacquet et al. 1992).

Marine insects: one species, 24-hour LC50, 0.71 µg/L, but this did not meet screening criteria.

Australian and New Zealand data

Unpublished Australian data range from 0.01 to 0.08 µg/L for Ceriodaphnia dubia (Warne pers. comm. 2000). These data were not used for calculations.

Factors causing variations in toxicity

The low water solubility and high log K_ow indicate that deltamethrin would be strongly bound to sediment or suspended matter and would be transient in the water column.

Guideline

The low water solubility of deltamethrin caused most of the data to be screened out. The exceptionally low figure for D. magna appeared anomalous and did not accord with recent Australian data on C. dubia. Hence the next lowest figure of 0.01 µg/L was used.

A low reliability freshwater trigger value of 0.0001 µg/L (0.1 ng/L) was derived for deltamethrin using the assessment factor (AF) method and a factor of 100. The freshwater figure could be adopted as a marine low reliability trigger value. This figure should be used only as an indicative interim working level.

References

ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Cacquet T, Thybaud E, LeBras S, Jonot O & Ramade F 1992. Fate and biological effects of lindane and deltamethrin in freshwater mesocosms. Aquatic Toxicology 23, 21-278.

Hill IR, Shaw JL & Maund SJ 1994. Review of aquatic field tests with pyrethroid insecticides. Chapter 15 in Freshwater field tests for hazard assessment of chemicals, eds IR Hill, F Heimbach, P Leeuwangh & P Matthiesson, Lewis Publishers, Boca Raton, FL, 249-271.

Maguire RJ, Carey JH, Hart JH, Tkacz RJ & Lee HB 1989. Persistence and fate of deltamethrin sprayed on a pond. Journal of Agricultural and Food Chemistry 37, 1153-1159.

Muir DCG, Yarechewski AL & Neal BR 1992. Influence of surface films on the fate of deltamethrin following serial application to prairie ponds. Environmental Toxicology and Chemistry 11, 581-591.

NRA 1997a. Database extraction of selected pesticides: Registered uses in Australia, National Registration Authority, July 1997, Canberra.

Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.