Thiram
(endorsed 2011)
Guideline
Based on human health concerns, thiram in drinking water should not exceed 0.007 mg/L.
Related chemicals
Thiram (CAS 137-26-8) belongs to the dimethyldithiocarbamate class of chemicals. Another pesticide in this class is ziram (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population is expected to be well below levels that may cause health concerns.
If present in drinking water as a result of a spillage or through misuse, thiram would not be a health concern unless the concentration exceeded 0.007 mg/L. Minor excursions above this level would need to occur over a significant period to be a health concern, as the health-based guideline is based on long-term effects.
With good water quality management practices, pesticides should not be detected in source waters used for drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.
General description
Uses: Thiram is used as a fungicide for the control of disease in turf, ornamentals, vines and agricultural crops or as an antifouling agent on industrial equipment and boats.
There are registered products that contain thiram in Australia. The products are intended for professional and/or home garden use and are available as concentrated solutions. They are applied diluted as a seed dressing prior to sowing, as a drench to seedbeds, or as a spray using hand-held or ground boom equipment. They are also applied as concentrated paint using brushes, rollers or air spray equipment. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to thiram and its metabolites are the use of home garden products, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of thiram may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
No data on the occurrence of thiram in Australian waters could be found. Thiram adsorbs strongly to soils. In the USA, thiram is predicted at concentrations of approximately 4.3 and 0.84 µg/L in surface water and groundwater, respectively (USEPA 2004).
Treatment of drinking water
No information on the efficiency of drinking water treatment processes to remove thiram could be found.
Measurement
Thiram in water can be analysed by a variety of methods (Sharma et al. 2003). Using high-performance liquid chromatography coupled with enrichment with a minicolumn allows determination of thiram to 0.5 µg/L (Suzuki et al. 1993).
History of the health values
The current acceptable daily intake (ADI) for thiram is 0.004 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.4 mg/kg bw/day from a long-term (2-year) dietary study in dogs. The NOEL is based on neurological disturbances, anaemia and changes in the liver. The ADI incorporates a safety factor of 100, and was established in 1995.
The previous ADI for thiram was 0.001 mg/kg bw. It was amended in 1995 following the evaluation of new studies that addressed the inadequacies of the toxicological database.
The previous health value was 0.003 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Thiram is well absorbed via the gastrointestinal tract and is widely distributed in tissues and blood. It is extensively metabolised and excreted mainly in expired air and urine, with smaller amounts detected in the faeces. The majority of the dose is eliminated within 48 hours in rats.
Acute effects: Thiram has low to moderate acute oral toxicity and low acute dermal toxicity. It is a skin sensitizer in guinea pigs and is associated with allergic dermatitis in humans following occupational use.
Short-term effects: Short-term dietary studies were conducted in mice, rats and dogs. In both mice and rats, there was reduced food consumption and reduced bodyweight gain at 25 mg/kg bw/day and above. In rats, there was also evidence of anaemia and changes in clinical chemistry parameters indicative of liver/kidney damage. Histopathological changes in the stomach at 25 mg/kg bw/day and degenerative changes in the testes at 90 mg/kg bw/day were also observed. In dogs, there were reduced erythrocyte counts at 2.3 mg/kg bw/day as well as other haematological and clinical chemistry changes at higher dose levels.
Long-term effects: Long-term dietary studies have been conducted in mice, rats and dogs. In mice, there was reduced bodyweight gain, evidence of anaemia and irritation of the stomach at 57 mg/kg bw/day and above. In rats, there was pancreatic atrophy, bile duct hyperplasia, and extramedullary haematopoiesis in the liver and spleen at 1.5 mg/kg bw/day and above. At higher doses, there was evidence of neurotoxicity, anaemia, and benign neoplastic lesions in the liver and thyroid. In dogs, there were clinical chemistry changes indicative of liver effects at 2.6 mg/kg bw/day. Histopathological changes in the liver, as well as anaemia and clinical signs of neurotoxicity, were reported at 4 mg/kg bw/day. At the highest dose of 40 mg/kg bw/day, clonic convulsions, severe anaemia and ophthalmological effects were reported. The NOEL for neurological, anaemic and liver effects in the dog was 0.4 mg/kg bw/day, and is the basis for the current ADI.
Carcinogenicity: Long-term dietary studies in rats reported benign neoplastic lesions in the liver, thyroid and retina. These effects occurred at doses well in excess of the likely level of human exposure.
Genotoxicity: Thiram produced both positive and negative results in in vitro and in vivo short-term assays. The weight of evidence indicates that it is weakly genotoxic.
Reproductive and developmental effects: A two-generation reproduction study in rats and developmental toxicity studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or foetal development.
Neurotoxicity: Short-term dietary studies in chicks and long-term dietary studies in rats and dogs reported symptoms indicative of nervous system toxicity, but only at dose levels well in excess of the likely level of human exposure.
Poisons Schedule: Thiram is included in Schedule 6 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010). Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.007 mg/L for thiram was determined as follows:
where:
0.4 mg/kg bw/day is the NOEL based on a long-term (2-year) study in dogs.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the assumption that 10% of the ADI will arise from the consumption of drinking water.
2 L/day is the estimated maximum amount of water consumed by an adult.
200 is the safety factor applied to the NOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation. With an additional safety factor of 2 to address the additional uncertainty in relation to the carcinogenicity of thiram.
References
NOTE: The toxicological information used in developing this fact sheet is from reports and data held by the Department of Health, Office of Chemical Safety.
DoHA (2010) The Poisons Standard; Schedule 1-Standard for the Uniform Scheduling of Medicines and Poisons, Department of Health and Ageing, Commonwealth of Australia, Canberra.
NHMRC (National Health and Medical Research Council), NRMMC (Natural Resources Management Ministerial Council) (2004). Australian Drinking Water Guidelines. National Water Quality Management Strategy, Paper 6. NHMRC and NRMMC.
Sharma VK, Aulakh JS, Malik AK (2003). Thiram: degradation, applications and analytical methods. Journal of Environmental Monitoring, 5:717-723.
Suzuki T, Yaguchi K, Kano I (1993). Screening methods for asulam, oxine-copper and thiram in water by high-performance liquid chromatography after enrichment with a minicolumn. Journal of Chromatography A, 643(1-2):173-179.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
USEPA (United States Environmental Protection Agency) (2004). Reregistration eligibility decision (RED) for Thiram. EPA 738-R-04-012. USEPA.
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