Proposed Adoption of the Canadian Water Quality Guideline for Arsenic as the Provincial Water Quality Objective

This notice was originally posted in the old Environmental Registry under number PA8E0022.

Description of policy

A Canadian Water Quality Guideline (CWQG) was approved for arsenic for the protection of aquatic life. Available information on the physical-chemical properties, aquatic toxicity, bioaccumulation potential, taste and odour characteristics and genotoxicity potential of arsenic were considered in developing the guideline.

Arsenic toxicity has been well studied. The literature indicated that acute effects for a variety of aquatic life occurred between 1.4 mg/L and 4700 mg/L for various forms of arsenic. Chronic effects ranged from 0.05 mg/L to 360 mg/L. Arsenic does not appear to bioaccumulate to any significant degree in fish. Vocke et al. (1980) reported that 0.05 mg/L caused a 50% inhibition of growth in the alga Scenedesmus obliquus. The safety factor of 10 was applied to this value to derive the CWQG. This CWQG will be adopted as the Provincial Water Quality Objective.

The recommended PWQO for total arsenic in water samples is 5 ug/L.

The proposed PWQO is above the current MOE routine laboratory detection limit of 1 ug/L. The value of 5 ug/L should be protective of effects due to aquatic toxicity. There are insufficient data to assess the mutagenic potential of arsenic to aquatic organisms. Data for mammalian systems indicates that arsenic is a fairly potent genotoxin and cogenotoxin that may induce teratogenic or carcinogenic effects. Therefore, the PWQO based on aquatic toxicity may not protect against these effects. It is therefore suggested that further research be done on such effects on aquatic organisms.

Purpose of policy

Contaminants that impair the aquatic environment are an important environmental concern. Provincial Water Quality Objectives are used to assist in managing these contaminants. The policies and procedures which govern their uses are contained in the booklet - Water Management (1994) - which deals with all aspects of Ontario's water management policy. Interim PWQOs are used to: i) classify receiving waters for water management purposes; ii) assess contaminant discharges to the aquatic environment; and iii) derive water quality-based effluent limits which may be included in Certificates of Approval which are issued to regulate effluent discharges.