Thiram 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
Thiram (CAS 137-26-8) is a dithiocarbamate fungicide introduced by DuPont and Bayer AG (Tomlin 1994). It acts by contact and protects foliage against fungal attack. Its IUPAC name is bis(dimethylthiocarbamoyl)disulfide. Its formula is C6H12N2S4 and molecular weight is 240.4. It is only slightly soluble in water to 18 mg/L and has a log Kow of 1.73. The current analytical practical quantitation limit (PQL) for thiram in water is 6 mg/L (NSW EPA 2000).
Uses and environmental fate
Thiram is used as a fungicide for grapes, vegetables, soft fruit, cotton, cereals and ornamentals and for seed treatment. It is also used for control of plant rust and storage diseases (Tomlin 1994), and is often used in combination with insecticides or other fungicides.
Thiram decomposes more readily at alkaline pH and its DT50 is estimated to exceed 120 days at pH 4, 18 days at pH 7, and 9 hours at pH 9, but its measured decomposition in sandy soil at pH 6.7 was only 0.5 days (Tomlin 1994).
Freshwater fish: 10 species, 48 to 96-hour LC50, 0.3 to 7500 µg/L. The most sensitive figure was for larvae of Cyprinus carpio; another publication reported a 48-hour LC50 of 4000 µg/L for this species. 96-hour LC50s of between 0.67 to 0.9 µg/L were reported for Mystus vittatus. Chronic NOEC (60 days) for mortality of Oncorhynchus mykiss of 0.56 µg/L and for growth of 0.32 µg/L. (Gammarus were most sensitive and Asellus, least). Chronic NOEC (21 d) to Daphnia magna: 5.6 µg/L for reproduction; 1 µg/L for growth.
Freshwater platyhelminthes: one species, 96-hour LC50, 48 µg/L.
Freshwater algae: three species, 72 to 96-hour EC50 of 1000 to 5500 µg/L; 5-day NOEC (growth) of 250 µg/L was reported.
Freshwater amphibians: two species, 48 to 96-hour LC50 of 13 to 1000 µg/L.
No marine data were available.
Factors that modify toxicity
No data were available.
A freshwater moderate reliability guideline figure of 0.2 µg/L was derived for thiram using the statistical distribution method with 95% protection and the default assessment factor (AF) of 10. The 99% figure is 0.01 µg/L and should be used as the trigger value for slightly to moderately disturbed systems. This is in order to protect fish from acute toxicity. In the absence of marine data, 0.01 µg/L was adopted as a low reliability marine trigger value, which should be used as an indicative interim working figure only.
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.
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.