Update: January 1996
Current Massachusetts Regulatory Limit
MMCL = 0.02 mg/L. ORS has adopted the MCL published by the U.S. EPA.
Federal Regulatory Limit
The MCL is based on the MCLG of 0.02 mg/L.
Basis for Criteria
The MCLG of 0.02 mg/L is derived based on the RfD presented below and assuming that a 70 kg adult ingests 2 L/day of drinking water. A relative source contribution factor of 20% is also incorporated into this value (57 FR 31776 (7-17-92)).
RfD: 2.2 x 10-3 mg/kg/day
UF: 100 (10 for intra-species; 10 for inter-species)
The RfD is based on the formation of cataracts in the eyes of rats. A No Observed Adverse Effects Level (NOAEL) of 0.22 mg/kg/day was identified from a 2-year dietary study in rats (Chevron Chemical Company, 1985). The NOAEL of 0.22 mg/kg/day is supported by the data from a study by Clark and Hurst (1970) which also established 0.22 mg/kg/day as the NOAEL in rats from a two-year feeding study (Fed Reg, 1990).
Diquat has been designated a Group D carcinogen based on a lack of information on its carcinogenicity.
PQL: 0.004 mg/L
U.S. EPA Method 549 (HPLC)
PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at http://www.epa.gov/safewater/methods/methods.html.
Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:
Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at http://www.epa.gov/waterscience/drinking/standards/dwstandards.pdf.
RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.
Chevron Chemical Company. 1985. MRDI No. 00145885, 00155474, 00160673. Available from U.S. EPA.
Clark, DG and Hurst, EW. January 1970. The toxicity of diquat. British Journal of Industrial Medicine. 27(1): 51-55.
Federal Register. July 25, 1990. Part II. Environmental Protection Agency. 40 CFR Part 141 et al. National Primary and Secondary Drinking Water Regulations; Synthetic Organic Chemicals and Inorganic Chemicals; Proposed Rule. (55 FR 30370)
Federal Register. July 17, 1992. Part III. Environmental Protection Agency. 40 CFR Parts 141 and 142. National Primary Drinking Water Regulations; Synthetic Organic Chemicals and Inorganic Chemicals; Final Rule. (57 FR 31776).