Ambient Water Quality Guidelines for Sulphate
Prepared pursuant to Section 2(e) of the
Original signed by Margaret
This document is one in a series that establishes ambient water quality guidelines for British Columbia. It is based on a review of all the available toxicological information at the time of preparation. The guidelines are safe conditions or levels that have province-wide application and are set to protect various water uses. This report sets guidelines for sulphate to protect drinking water and freshwater aquatic life. No Canadian Council of Ministers of the Environment (CCME) guidelines for sulphate have been recommended or are anticipated at this time.
A major use of the guidelines is to set ambient water quality objectives. The objectives are the guidelines modified or adopted to protect the most sensitive designated water use in a particular body of water. The objectives are used in the preparation of waste management plans, pollution prevention plans, waste management permits, orders, or approvals. The latter three are the only documents that have legal standing.
The guidelines are summarized in Table 1 below.
THE MINISTRY OF ENVIRONMENT, LANDS AND PARKS (now called Ministry of Water, Land and Air Protection) develops province-wide ambient water quality guidelines for variables that are important in the surface waters of British Columbia. This work has the following goals:
Ambient water quality objectives for specific waterbodies will be based on the guidelines and also consider present and future uses, waste discharges, hydrology/limnology/oceanography, and existing background water quality. The process for establishing water quality objectives is more fully outlined in Principles for Preparing Water Quality Objectives in British Columbia, copies of which are available from Water Quality Section of the Water Management Branch.
Neither guidelines nor objectives which are derived from them, have any legal standing. The objectives, however, can be used to calculate allowable limits or levels for contaminants in waste discharges. These limits are set out in waste management permits and thus have legal standing. The objectives are not usually incorporated as conditions of the permit.
The definition adopted for a guideline is:
The guidelines are province-wide in application, are use-specific, and are developed for some or all of the following specific water uses:
The guidelines are set after considering the scientific literature, guidelines from other jurisdictions, and general conditions in British Columbia. The scientific literature gives information on the effects of toxicants on various life forms. This information is not always conclusive because it is usually based on laboratory work which, at best, only approximates actual field conditions. To compensate for this uncertainty, guidelines have built-in safety factors which are conservative but reflect natural background conditions in the province.
The site-specific water quality objectives are, in most cases, the same as guidelines. However, in some cases, such as when natural background levels exceed the guidelines, the objectives could be less stringent than the guidelines. In relatively rare instances, for example if the resource is unusually valuable or of special provincial significance, the safety factor could be increased by using objectives which are more stringent than the guidelines. Another approach in such special cases is to develop site-specific guidelines by carrying out toxicity experiments in the field. This approach is costly and time-consuming and therefore seldom used.
Guidelines are subject to review and revision as new information becomes available, or as other circumstances dictate.
Sulphur is a non-metallic element that occurs naturally in numerous minerals, including barite (BaSO4), epsomite (MgSO4·7H2O), and gypsum (CaSO4·2H2O). Hexavalent sulphur combines with oxygen to form the divalent sulphate ion (SO42-). The reversible reaction between sulphide and sulphate in the natural environment is often referred to as the "sulphur cycle".
Natural sources of sulphur include volcanoes, decomposition and combustion of organic matter, and from sea salt over the oceans. Particles of sea salt formed by the breaking of myriads of bubbles are an important source of atmospheric sulphate. The atmosphere is the main vehicle for transport of sulphur from various sources.
Sulphates are discharged into the aquatic environment in wastes from industries that use sulphates and sulphuric acid, such as mining and smelting operations, kraft pulp and paper mills, textile mills and tanneries. Iron sulphides (e.g., FeS) may be exposed to water and atmospheric oxygen by mining or rock excavation, producing sulphuric acid, which contributes sulphate to ground and surface surface waters. Sulphates are also released during blasting and the deposition of waste rock in dumps at metal mines. This is known as acid rock drainage and is a significant source of sulphate generation in British Columbia. The burning of fossil fuels is also a major source of sulphur to the atmosphere. Most of man's emissions of sulphur to the atmosphere, about 95%, are in the form of SO2. Sulphate fertilizers are also a major source of sulphate to ambient waters.
Sulphate concentrations typically range between about 2 and 30 mg/L for most lakes and rivers in British Columbia. Although, some lakes in the Cariboo Region and in Richter Pass near Osoyoos have particularly high natural sulphate levels in the thousands of mg/L. Seasonal fluctuations in dissolved sulphate concentrations are obvious in most rivers, with low concentrations during freshet and elevated concentrations during winter low flows.
Seawater typically contains about 2700 mg/L sulphate and it has been estimated that about 1.7 million tonnes of sulphate are added annually to the Canadian atmosphere from sea spray.
A few studies have reported sulphate toxicity to some aquatic organisms, including some fish and aquatic mosses at concentrations at or below 100 mg/L SO4. However, there was some question as to the reliability of these data for a number of reasons such as poor laboratory test procedures, failure to report crucial test procedure information, or calculation errors.
In a recent series of bioassays performed specifically for this review, the lowest SO4 effect level reported was 205 mg/L to a species of freshwater invertebrate in soft water.
Sulphate water quality guidelines were not considered necessary for water uses other than those recommended here.
These guidelines are based on a comprehensive review of the available toxicological data for sulphate compiled in the Technical Appendix and are designed to suit BC conditions. The recommended BC Guidelines are summarized in Table 1.
A concentration of up to 500 mg/L sulphate in water to be used for drinking is adopted from the BC Ministry of Health and Health Canada recommended drinking water guideline for sulphate as it is dispensed at the consumer's tap. This is an aesthetic objective based on taste considerations. Health Canada also advises that concentrations exceeding 500 mg/L may cause a laxative effect in some individuals.
We adopt this same concentration as a drinking water quality guideline for ambient waters. Even with advanced water treatment, other than reverse osmosis, sulphate concentrations will not be reduced at the consumer's tap.
To protect freshwater organisms in British Columbia, a water quality guideline of 100 mg/L for dissolved sulphate, measured as SO4, is recommended. This guideline is a maximum concentration that should not be exceeded at any time.
There is conflicting evidence over the sensitivity of aquatic mosses to sulphate. Therefore, it is recommended that for waterbodies with concentrations of dissolved sulphate that exceed 50 mg/L as a result of anthropogenic sources, the health of aquatic moss populations should be checked on an occasional basis.
The guideline is based primarily on three studies which investigated the effects of sulphate on freshwater organisms. These are as follows:
There is some evidence that increased water hardness ameliorates sulphate toxicity which may allow for a site-specific sulphate objective that is less stringent than the guideline recommended here. To adjust the guideline recommended here to take local conditions into consideration, the BC Ministry Of Environment, Lands and Parks publication, "Methods for Deriving Site-Specific Water Quality Objectives in British Columbia and Yukon" should be followed.