Captan

(endorsed 2011)

Guideline

Based on human health concerns, captan in drinking water should not exceed 0.4 mg/L.

Related chemicals

Captan (CAS 133-06-2) belongs to the phthalimide class of chemicals. There are currently no other pesticides in this class in use (Tomlin 2006).

Human risk statement

With good water quality management practices, 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, captan would not be a health concern unless the concentration exceeded 0.4 mg/L. Excursions above this level even for a short period are of concern as the health-based guideline is based on short-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: Captan is a fungicide for the control of fungal diseases in turf, ornamentals, agricultural crops and seedlings.

There are registered products that contain captan in Australia. These products are intended for professional use and are available as water-dispersible granules or as a dust. Captan is applied to turf, ornamentals, and agricultural crops as a dilute or concentrated spray using ground or hand-held equipment. Captan is applied as a powder to seedlings. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.

Exposure sources: The main source of public exposure to captan is residues in food. Residue levels in food produced according to good agricultural practice are generally low.

Agricultural use of captan 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 published reports on captan occurrence in Australian drinking water supplies were found. In the Nile river, captan has been found at 0.0003 mg/L (0.3 μg/L) (Abbassy et al. 1999).

Treatment of drinking water

Captan can be degraded by ozone, ultraviolet (UV) irradiation and chlorine. Destruction of captan in water using short wavelength UV light has been reported (Peterson et al. 1990). Captan is also rapidly degraded in 50 and 500 mg/L chlorine solutions at pH 7 and 10.7 (Ong et al. 1996). Ozonation is effective in degrading captan and degradation rates increased at higher pH and temperature (Ong et al. 1996).

Measurement

Captan can be extracted by liquid/liquid extraction with dichloromethane. The extract is dried with sodium sulfate, concentrated, and analysed by gas chromatography–mass spectrometry in selected ion monitoring mode. The method can achieve a limit of detection (LOD) of 0.0005 mg/L (0.5 μg/L). Captan can also be extracted using solid-phase extraction (SPE) and measured using high performance liquid chromatography (HPLC) (Marvin et al. 1990, Wang et al. 2007) or gas chromatography/negative chemical ionization-mass spectrometry (Barreda et al. 2006). A fully automated system for on-line SPE followed by HPLC with tandem detection with a photodiode array detector and a fluorescence detector (after post-column derivatisation) can achieve a LOD of 0.001 mg/L (1 μg/L) (Patsias and Papadopoulou-Mourkidou 1999).

Trace-level determination of captan can be achieved by solid-phase micro-extraction and gas chromatography coupled with electron-capture detection (LOD=0.000015 mg/L [0.015 μg/L]) or with mass spectrometric detection (LOD=0.00004 mg/L [0.04 μg/L]) (Lambropoulou et al. 2000). Captan can be analysed by EPA Method 617 (Determination of organohalide pesticides and PCBs in industrial wastewater) using electron capture gas chromatography or EPA Method 8081A (Organochlorine pesticides, by gas chromatography: capillary column technique) using electron capture detector or an electrolytic conductivity detector.

An optical biosensor consisting of a glutathione-S-transferase-immobilized gel film can detect captan in contaminated water at 0.002 mg/L (2 μg/L) (Choi et al. 2003). A spectrophotometric method for the determination of captan based on its reaction with thiosemicarbazide can achieve a LOD of 0.0005 mg/L (0.5 μg/L) at an absorbance of 315 nm (Galeano et al. 2002).

History of the health values

The current acceptable daily intake (ADI) for captan is 0.1 mg per kg body weight (mg/kg bw), based on a no-observed-effect level (NOEL) of 10 mg/kg bw/day from a short-term (developmental toxicity) study in rabbits. The NOEL is based on decreased bodyweight and food consumption in dams and associated foetotoxicity at 30 mg/kg bw/day and above. The ADI incorporates a safety factor of 100, and was established in 1997.

The acute reference dose (ARfD) of 0.1 mg/kg bw/day for captan was established in 1997, based on a NOEL of 10 mg/kg bw/day from a developmental study in rabbits. The ARfD incorporates a safety factor of 100.

A health value has not been previously established by NHMRC.

Health considerations

Metabolism: Captan is well absorbed via the gastrointestinal tract in mice and rats. In rats, the highest levels were found in kidneys, liver, blood or gastrointestinal tract, particularly in the distal small intestine. In mice, higher levels were found in the duodenum and large intestine. In mice and rats, captan is rapidly and extensively excreted. In mice, captan is excreted in the urine as metabolites (44%), in the faeces mostly unchanged (22%), and in expired air as CO2 (19%). In rats, captan is extensively metabolised and rapidly excreted mostly in the urine (80-90%) and the remainder in the faeces. The major urinary metabolites in both mice and rats were thiazolidine-2-thione-4-carboxylic acid (TTCA) and dithiobis-methanesulfonic acid derivatives.

In human volunteers captan was rapidly excreted in urine as TTCA (4-9%) and tetrahydrophthalimide (THPI) (1-3%).

Acute effects: Captan has low acute oral and dermal toxicity. It is a skin sensitiser in both laboratory animals and humans.

Short-term effects: Short-term dietary studies in mice reported dose-related hyperplasia in the duodenum and associated inflammatory cell response at doses of 120 mg/kg bw/day and above. Decreased bodyweight gain, and hyperplasia and hypertrophy in the glandular forestomach were reported at higher doses.

Long-term effects: Long-term dietary studies in mice reported a dose-related increase in the incidence of hyperplastic lesions and benign and malignant tumours in the duodenum at 122 mg/kg bw/day. At higher doses, there was also an increase in benign and malignant tumours in the jejunum/ileum. In long-term dietary studies in rats, decreased bodyweight gain was observed at 96 mg/kg bw/day. Long-term dietary studies in dogs reported no treatment-related effects up to doses of 300 mg/kg bw/day.

Carcinogenicity: Long-term studies in rats provide no evidence of carcinogenicity for captan. In long-term studies in mice, tumours in the duodenum were observed but were considered to occur via an inflammatory mechanism specific to mice, and were reported at dose levels well in excess of the likely level of human exposure.

Genotoxicity: Captan was positive in some in vitro short-term assays, but overall it was not considered to be genotoxic.

Reproductive and developmental effects: One and three-generation reproduction studies in rats did not produce evidence of reproductive toxicity. In developmental toxicity studies in rabbits, there was no effect on the foetus at doses that were not maternotoxic. These doses are well in excess of the likely level of human exposure in drinking water. The most sensitive effects reported were decreased bodyweight and food consumption in dams, and in the foetus there was an associated increased incidence of cysts on the liver and increased number of skeletal variations at doses of 30 mg/kg bw/day and above. The NOEL for these effects was 10 mg/kg bw/day, and this is the basis for the current ADI.

Poisons Schedule: Captan 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 0.4 mg/L for captan was determined as follows:

$$\text{ 0.4 mg/L   } = \dfrac{\text{ 10 mg/kg bodyweight/day x 70 kg x 0.1   }}{\text{ 2 L/day x 100   }}$$

where:

• 10 mg/kg bw/day is the NOEL based on a short-term (developmental toxicity) study in rabbits.

• 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.

• 100 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.

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.

Abbassy MS, Ibrahim HZ, el-Amayem MM (1999). Occurrence of pesticides and polychlorinated biphenyls in water of the Nile river at the estuaries of Rosetta and Damiatta branches, north of Delta, Egypt. Journal of Environmental Science and Health B, 34(2):255-67.

Barreda M, Lopez FJ, Villarroya M, Beltran J, Garcia-Baudin JM, Hernandez F (2006). Residue determination of captan and folpet in vegetable samples by gas chromatography/negative chemical ionization-mass spectrometry. Journal of AOAC International, 89(4):1080-7.

Choi JW, Kim YK, Song SY, Lee IH, Lee WH (2003). Optical biosensor consisting of glutathione-S-transferase for detection of captan. Biosensors and Bioelectronics, 18(12):1461-6.

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.

Galeano T, Guiberteau A, Mora NM, Alvarez PR, Salinas F (2002). Spectrophotometric determination of the fungicide captan. Journal of Environmental Science and Health B, 37(6):533-40.

Lambropoulou DA., Konstantinou IK, Albanis TA.(2000). Determination of fungicides in natural waters using solid-phase microextraction and gas chromatography coupled with electron-capture and mass spectrometric detection. Journal of Chromatography A, 893(1):143-56.

Marvin CH, Brindle ID, Hall CD, Chiba M (1990). Development of an automated high-performance liquid chromatographic method for the on-line pre-concentration and determination of trace concentrations of pesticides in drinking water. Journal of Chromatography, 503(1):167-76.

Ong KC, Cash JN, Zabik MJ, Siddiq M, Jones AL (1996) Chlorine and ozone washes for pesticide removal from apples and processed apple sauce. Food Chemistry, 55(2):153-160(8).

Patsias J, Papadopoulou-Mourkidou E (1999). A fully automated system for analysis of pesticides in water: on-line extraction followed by liquid chromatography-tandem photodiode array/postcolumn derivatization/fluorescence detection. Journal of AOAC International, 82(4):968-81.

Peterson D, Watson D, Winterlin W (1990). Destruction of pesticides and their formulations in water using short wavelength UV light. Bulletin of Environmental Contamination and Toxicology, 44(5):744-50.

Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.

Wang S, Yu Y, Tan P, Miao Z, Wei Y (2007) [Simultaneous determination of captan and folpet pesticide residues in apples by solid-phase extraction and high performance liquid chromatography]. Se Pu, 25(2): 226-9.