Carbofuran 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

Carbofuran (CAS 1563-66-2) is a carbamate insecticide and nematicide, introduced by Bayer. It has systemic action by contact and ingestion (Tomlin 1994). Its IUPAC name is 2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate. Its formula is C₁₂H₁₅NO₃ and molecular weight is 221.3. It is soluble in water to 320 mg/L at 20°C and has a log K_ow of 1.52. Carbofuran is a cholinesterase inhibitor. The current analytical practical quantitation limit (PQL) for carbofuran in water is 2 µg/L (NSW EPA 2000).

Uses and environmental fate

Carbofuran is used to control leaf and soil insects and nematodes in a variety of fruit, vegetable and cereal crops (Tomlin 1994). In Australia it has around 10 registered uses in rice, sugarcane, tobacco and wheat (NRA 1997a). It is stable in acid or neutral media but unstable at higher pH. Its DT50 at pH 7 was 120 d, but was reduced to 31 d at pH 9 (Tomlin 1994).

Aquatic toxicology

Freshwater fish: 24 species, 48-96 h LC50, 80-4800 µg/L. There were some individual high outlying figures for individual species, Cyprinus carpio (11 mg/L), Lepomis macrochirus (311 mg/L), Oncorhynchus mykiss (8.5 mg/L) and Tilapia mossambica (31 mg/L). Chronic NOEC figures for O. mykiss (90-d mortality, 24.8 µg/L, giving an ACR of 15.3) and Pimephales promelas (31-d mortality, 68 µg/L).

Freshwater amphibians: two species, 96-h LC50, 13,470-133,200 µg/L (also a single lower figure of 110 µg/L).

Freshwater crustaceans: six species, 48-96 h LC50 or EC50 (immobilisation), 0.33 (freshwater prawn Caridina rajadhari) to 86 µg/L (three other species were ≤2.5 µg/L: Paratelphusa jacquemontii crab 48-96 h LC50 1.6 µg/L; Ceriodaphnia dubia 48-96 h LC50 2.4 µg/L). An additional three species were much less sensitive at 96 h, Macrobrachium kistnensis (157 µg/L), crab Oziotelphusa senex senex (31,100-44,600 µg/L) and crayfish Procambarus acutus acutus (500 µg/L). A chronic NOEC for waterflea Ceriodaphnia dubia (7 d, mortality) was 1.3 µg/L, giving an acute-to-chronic ratio (ACR) of 2. A 50-d NOEC for crab Cancer magister was 0.5 µg/L—this may apply to marine systems but could not be checked.

Freshwater insects: one species, 48-h EC50, 56 µg/L.

Freshwater molluscs: 1 sp, 96-h LC50, 3808 µg/L.

Freshwater annelids: two species, 96-h LC50, 5300-14,000 µg/L.

Freshwater algae: one species, 96-h EC50, population growth, 204,500 µg/L.

Marine fish: two species, 48-96 h LC50, 100-390 µg/L.

Marine crustacean: two species, 96-h LC50, 1.5-4.7 µg/L (values for adults were 21-190 µg/L). A chronic NOEC for Cancer magister (90 d mortality) for adults was 25 µg/L.

Factors that modify toxicity

None were identified.

Guideline

An overall ACR of 4.9 was used. The default ACR did not reduce the 95% protection level below the LC50 for the most sensitive crustacean species. A freshwater moderate reliability guideline figure of 1.2 µg/L was derived for carbofuran using the statistical distribution method at 95% protection and an ACR of 4.9. However, this did not adequately protect some crustaceans from acute toxicity and the 99% protection level of 0.06 µg/L is recommended as the trigger value for slightly-moderately disturbed systems. Given the limited marine data, a marine low reliability trigger value of 0.06 µg/L was adopted from the 99% protection freshwater figure. This should be used as an indicative interim working level only.

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.

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

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

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