Diuron in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems
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
Diuron (CAS 330-54-1) is a selective urea herbicide, developed by DuPont, which has a systemic mode of action, being mainly absorbed through the roots (Tomlin 1994). It inhibits photosynthesis. Its IUPAC name is 3-(3,4-dichlorophenyl)-1,1-dimethylurea, its molecular formula is C9H10Cl2N2O, and molecular weight is 233.1. Diuron is soluble in water to 42 mg/L at 25°C (Tomlin 1994) and its log Kow is 2.8 and log Koc is 2.6 to 2.9.
Uses and environmental fate
Diuron has a wide variety of uses including total weed control in commercial areas, roads and railways and rights-of-way and selective control of grasses and broadleaf weeds in crops (Tomlin 1994). In Australia, diuron has around 2200 registered uses, including around 25 crops, cereals, vegetables, orchards and plantations, and flower nurseries as well as commercial areas, weed control in flood mitigation channels and as a boat antifoulant (NRA 1997a). Its use in drainage channels is restricted, at least in NSW (SPCC 1985).
Diuron persists in soils, with a DT50 of 90 to 180 days (Tomlin 1994), and in sediment. Under normal use it will remain active in soil for 4 to 8 months (Peterson & Batley 1991). It has been detected frequently in surface waters of the Murray-Darling Basin, usually between 0.2 and 3 µg/L (Cooper 1996). Adsorption by sediments increased with organic content of the sediment and temperature. Peterson and Batley (1991) used a model to predict a half-life of diuron in a lagoon of around 175 days, and 90% would be in sediment.
Freshwater fish: 15 species, 48 to 96-hour LC50, 500 to 63,000 µg/L. An additional species, Rasbora heteromorpha, had 48-hour LC50 of 190,000. An outlying figure of 84,000 µg/L was reported for Pimephales promelas, an order of magnitude greater than the next highest for this species. Chronic 64-day no observed effect concentration (NOEC) for P. promelas (mortality) was 33.4 µg/L, giving an ACR of 596.
Freshwater crustaceans: six species, 48 to 96-hour LC50, 160 to 15,500 µg/L.
Freshwater insects: two species, 48 to 96-hour LC50, 1200 to 3600 µg/L.
Freshwater algae: no data.
Marine fish: one species, 48-hour LC50, 6300 µg/L.
Marine molluscs: one species, 96-hour EC50 (growth), 1800 µg/L.
Factors that affect toxicity
Temperature changes did not affect toxicity of diuron to rainbow trout, Oncorhynchus mykiss (2°C to 18°C), and bluegills (7°C to 24°C). Toxicity was not affected by pH (6.4 to 8.5) or hardness (44 to 300 mg/L CaCO3) (Johnson & Finley 1980). Ageing of test solutions for 2 to 4 weeks decreased toxicity of diuron to fish by up to 9 times (Johnson & Finley 1980).
A freshwater low reliability trigger value of 0.2 µg/L was calculated for diuron using an assessment factor (AF) of 200 on the lowest of a limited set of chronic data. A marine low reliability trigger value of 1.8 µg/L was calculated for diuron using an AF of 1000. These figures should only be used as indicative interim working levels.
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.
Cooper B 1996. Central and north west regions water quality program 1995/96 Report on pesticides monitoring. Department of Land and Water Conservation, TS 96.048, Parramatta, NSW.
Johnson WW & Finley MT 1980. Handbook of acute toxicity of chemicals to fish and aquatic invertebrates. US Department of the Interior, Fish and Wildlife Service, No 137, Washington DC.
NRA 1997a. Database extraction of selected pesticides: Registered uses in Australia, National Registration Authority, July 1997, Canberra.
Peterson SM & Batley GE 1991. Fate and transport of endosulfan and diuron in aquatic ecosystems. Final Report AWRAC Project 88/20, CSIRO, Centre for Advanced Analytical Chemistry, Menai, NSW.
SPCC 1985. Priority issues involved in the diffuse pollution of waterways, especially by agricultural chemicals. Technical Advisory Committee Report, State Pollution Control Commission, Sydney.
Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.