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Water Quality Ambient Water Quality Guidelines for Toluene Overview Report Prepared pursuant to Section 2(e) of the Original signed by Margaret
Eckenfelder
This document is one in a series that establishes ambient water quality guidelines for British Columbia. It is based on a technical report prepared for the Canadian Council of Ministers of Environment (CCME) proposing Water Quality Guidelines for Toluene (July 1995 update). This overview report assesses those guidelines for use in British Columbia, assesses more recent information and makes amendments where appropriate to suit BC conditions. 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 toluene to protect drinking water, freshwater and marine aquatic life and livestock watering. Based on this evaluation, the CCME guidelines adopted by the province were for drinking water and livestock watering, while adjustments were deemed necessary to protect aquatic life in fresh and marine waters. 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 status. The guidelines are also used as a basis for evaluating contaminated sites and determining remediation requirements. The guidelines are summarized in Table 1. Table 1: Summary of Water Quality Guidelines for Toluene
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.
Toluene is a colourless liquid at room temperature with a gasoline-like aroma. It occurs naturally in coal and crude oil and is found in consumer products such as paints, cosmetics, upholstery, carpet cleaners, cigarette smoke, pesticides and gasoline. In Canada, toluene is used in the production of benzene and as an octane enhancer instead of lead in gasoline refining. Toluene can enter aquatic environments during production, usage, storage, transportation and spills. Toluene has been detected throughout North America in effluents from municipalities, industries, industrialized river basins, ground water, sediments, soil and water. It is released into the air from burning oil, gas and coal. Physical, biological and chemical processes remove toluene from all media so there is little tendency for it to accumulate in environmental compartments. Toluene can be removed from water by volatilization and biodegradation, but does not tend to hydrolyze or adsorb to sediments. It may leach into ground water if released to land. Toluene is volatile with a half-life of up to two weeks in water. The log octanol-water partition coefficient, Kow, is 2.7. The CCME noted that the following toxicity tests (lowest value shown) from the literature were deemed as primary: Table 2: Freshwater Toxicity Tests
The results from static renewal testing undertaken by BC Environment in partnership with the Canadian Petroleum Producers Institute in 1999 for Daphnia magna at a nominal hardness of 100 mg/L CaCO3 are as follows:
These guidelines are based on a review of the technical background information used to prepare the CCME Water Quality Guidelines for Toluene, July 1995 update, as well as recent information from the literature and other sources. The guidelines have been revised where appropriate to suit BC conditions, and are summarized in Table 1.
An aesthetic objective of 0.024 mg/L for toluene in drinking water has been recommended by the Federal-Provincial Subcommittee on Drinking Water, Health Canada, 1993 and is adopted for ambient conditions.
This concentration yields no objectionable taste or smell and no adverse health effects. Without treatment prior to entering a water distribution system, toluene concentrations will change little from ambient concentrations, especially when the time from withdrawal to use is short. Therefore, the recommended concentration for water distribution systems will be the ambient water quality concentration for toluene.
The maximum concentration of toluene should not exceed the BC guideline of 0.039 mg/L. This guideline has been revised from the CCME guideline of 0.002 mg/L.
We found that the data quality from the researchers was considered by CCME to be as satisfactory, ranked primary data, based on the requirements of the CCME Protocol. However, using the same Protocol, we have applied professional judgement since we have serious concerns about the results for the species used in guideline development by CCME. The CCME guideline was established using the most sensitive species for an early life stage chronic test for rainbow trout, Oncorhynchus mykiss. The results are in a 1982 research paper from the University of Kentucky that is not widely available. This 27-d LC50 was 0.02 mg/L, twenty times more sensitive than reported by the same authors for the leopard frog, Rana pipiens, or forty times more sensitive than the next most sensitive species that they reported, a salamander, Ambystoma gracile. In fact, the most sensitive species reported by independent researchers was for coho salmon, Oncorhynchus kisutch, with a 40-d weight decrease at 2.8 mg/L toluene, which is 140 times higher than the study used by CCME. All other authors report even higher concentrations for other species. The difficulty in testing toluene due to its volatility can lead to problems in getting accurate toxicity measurements. For this reason, we believe that results from a flow-through test with constant replacement are the ideal. Unfortunately, the results in the literature do not always meet this ideal. Since the rainbow trout, Oncorhynchus mykiss, study that reported the 27-d LC50 of 0.02 mg/L was a flow-through test, we examined the acute to chronic ratios where available for the same species. We know on the basis of the CCME Protocol that the acute/chronic ratio should be about 2:1 for most species since the application factor recommended by CCME is 0.05 for acute data and 0.10 for chronic data. The actual ratios calculated from data in the literature were: Table 5: Acute to Chronic Ratios
The chronic data themselves seem quite low in comparison to other work. The principle investigators have published toxicity data for other variables that we have questioned in the past. These include data for copper which were reported as causing skeletal defects in the range from 1-5 µg/L but in the same paper, these researchers proposed a copper guideline at the 3-5 µg/L level. We find this interesting since the authors did not suggest that a guideline was needed to protect the most sensitive effect levels and that no safety factor was needed. Although the research for the critical paper was reported in 1982, there have been no further studies reported in the literature on rainbow trout that yielded comparable results. This in itself seems strange. BC Environment, with the help of the Canadian Petroleum Producers Institute (CPPI), arranged for tests to be done through Environment Canada on early life stage rainbow trout, Oncorhynchus mykiss, and Daphnia magna. The tests unfortunately were not flow-through in nature, but static renewal tests and did not yield results for rainbow trout that we deemed to be helpful in establishing a guideline. The results for testing Daphnia magna are presented above. We therefore question the validity of the rainbow trout chronic data. This is based on its low concentration relative to other work, the extremely high ratio produced in relation to acute studies, which seem to be of the right order-of-magnitude, and the fact that no other researchers have reproduced the results in the last twenty years. Of interest is the fact the US EPA has an alert level of 17.5 mg/L, while Quebec has a chronic guideline of 0.026 mg/L and an acute guideline of 0.58 mg/L. In developing their guideline, the CCME applied a safety factor of 10:1. This was appropriate since toluene has high volatility, the guideline was based on a chronic study, toluene has low bioaccumulation potential and would not be expected to remain in the environment for prolonged periods of time. The half-life is up to two weeks in water. The LOEC/NOEC ratio for freshwater aquatic life, fathead minnow, is low, 1.5:1. We therefore used the next most sensitive species from the literature, the leopard frog, Rana pipiens, which had a 9.5-d LC50 of 0.39 mg/L and applied the safety factor of 10:1 to produce a guideline of 0.039 mg/L. Although the research was performed by the same researchers as produced the data for rainbow trout, we do not have as much information available (e.g., no acute/chronic ratio) on which to refute these data which are still approximately one order of magnitude lower than the next independent tests. We have no acute to chronic ratios, data from no other researchers on the leopard frog, or data for other similar species or data for other chemical compounds that might help us to validate the data. Therefore, we use the Ministry's precautionary principle in accepting these data at this time. By so doing, this yields a guideline of 0.039 mg/L that is about twice the level of concern raised for rainbow trout.
The maximum concentration of toluene should not exceed 0.33 mg/L. This guideline has been revised from the CCME guideline of 0.21 mg/L.
The critical study used by the CCME to derive the guideline was classified as secondary data. In BC, we eliminated this study for determining the BC guideline, since the concentrations reported for the test were not measured but were estimated. The next lowest critical study with measured values had a 96-h LC50 of 6.52 mg/L for pink salmon, Oncorhynchus gorbuscha. We maintained the safety factor used by CCME of 20:1 for BC based on not having a chronic study or a LOEC to NOEC ratio. Although toluene has a relatively short half-life and low potential to bioaccumulate, a safety factor of 0.05 was applied to the reference level for three reasons:
No water quality guideline for this use is recommended, as there are insufficient data on the adverse effects of toluene in irrigation water.
Guidelines for livestock watering for BC are the same as for CCME, 0.024 mg/L. Toluene is a very volatile substance. The water quality guidelines recommended in this document are based primarily on controlled, laboratory bioassays that do not account for factors that may modify the toxicity of toluene in the field.
Care must be exercised when the water quality guidelines are applied to assess environmental impacts of toluene, since there will be situations where toluene concentrations are continuously renewed, e.g., discharge from an industrial operation, or with the potential for only a minimal amount of volatilization e.g., under ice cover. In these types of situations, a site-specific study should be undertaken and appropriate site-specific water quality objectives developed based on species present and actual toluene persistence and concentrations. In many cases, water quality objectives will be the same as the guidelines. When concentrations of toluene in developed waterbodies are constantly maintained due to a continuous source or an environmental condition that prevents its degradation, then water quality objectives that are more stringent than the recommended guidelines may be justified. In some cases, socioeconomic or other factors may justify objectives that are less stringent than the guidelines. Site-specific impact studies would be required in such cases. Methods (e.g., water effects ratio, resident species toxicity in the field, etc.) are available to adapt the recommended guidelines to a given site by considering these factors. Where necessary, these methods can be employed to set site-specific water quality objectives. Because these approaches are costly and time consuming, they are seldom used.
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