Ambient Water Quality Guidelines for Chlorophenols

Water Quality

Ambient Water Quality Guidelines for Chlorophenols

6. DRINKING WATER

6.1 General

The major effect of chlorophenols, and PCP in particular, is to uncouple oxidative phosphorylation; this results in inhibition or greatly decreased efficiency in converting ingested food to energy and useful products. This is an essential process in all aerobic organisms, and death will result if the process is stopped. Since the effects on all animals, including people, are essentially the same, and are discussed in Chapter 7 on terrestrial animals they are not repeated here; nor are effects on people singled out and treated separately. Such effects have virtually no bearing on the setting of human drinking water guidelines since organoleptic effects occur at lower concentrations than acute or chronic toxic effects, and such taste and odour effects determine the drinking water guidelines. If one can not taste or smell chlorophenols in the water, there is no health risk and there is also a safety margin over the lowest concentration found to cause a health risk.

6.2 Taste and Odour

Chlorophenols are responsible for taste and odour problems in water; such effects are limiting in determining guidelines, since they occur below the LC₅₀ values for organisms (335). The actual guidelines suggested by various agencies for chlorophenols are in the µg/L range, lower than any observed physiological effect level, even after safety factors are applied to the results of taste and odour test panels to allow for more sensitive people in the general population. Tables 6.2.1 and 6.2.2 give some taste and odour thresholds for chlorophenols in water. These tend to be temperature dependent since temperature affects the volatility of chlorophenols. The lowest taste or odour threshold is highlighted in bold type, and given first, for each chlorophenol congener. Taste thresholds tend to be one or two orders-of-magnitude lower than odour thresholds and, since these data are derived using human test panels and water with different characteristics, there is a large amount of variability in the results.

2-MCP, 3-MCP, 4-MCP, 2,4-DCP and 2,4,6-TCP

Taste and odour problems in drinking water are reportedly caused by these chlorophenols at very low concentrations in drinking water, in the µg/L range (183, 362, 366, 335, 372), but reference 183 reported little effect by 4-MCP and 2,4,6-TCP at these low levels.

6.3 Literature Guidelines

Table 6.3 lists published guidelines for various chlorophenols in drinking water. The most current Canadian guidelines for taste and odour of chlorophenols, by Health and Welfare Canada in 1989 (690), are the same as those in 1987 (110): 30 µg/L for PCP, 1 µg/L for 2,3,4,6-TTCP, 2 µg/L for 2,4,6-TCP and 0.3 µg/L for 2,4-DCP. No guidelines are set for the MCPs. CCME (CCREM) adopted these 1987 Health and Welfare guidelines.

The WHO guidelines for 1984 (225) are all 1 µg/L, including 2-MCP and 4-MCP. Taste thresholds appear to be one or two orders-of-magnitude lower than odour thresholds (225). The MCPs are less toxic than their more chlorinated congeners, but there are data to suggest that their taste thresholds could be as low as 0.1 µg/L (335).

6.4 Recommended Guidelines

We recommend adoption of the existing Canadian Drinking Water Quality Guidelines for Chlorophenols which have been adopted by the BC Ministry of Health (110, 690), with the addition of a monochlorophenol guideline of 0.1 µg/L (335). The existing Canadian Guidelines only specify specific isomers and omit any mention of others; we have set the guidelines based on the total concentration of all the isomers for each group of chlorophenols.

Aesthetic Guidelines (taste and odour)

The combined concentrations of all the monochlorophenols, MCPs, should not exceed 0.1 µg/L in raw drinking water (335).

The combined concentrations of all the dichlorophenols, DCPs, should not exceed 0.3 µg/L in raw drinking water .

The combined concentrations of all the trichlorophenols, TCPs, should not exceed 2 µg/L in raw drinking water .

The combined concentrations of all the tetrachlorophenols, TTCPs, should not exceed 1 µg/L in raw drinking water .

The concentration of pentachlorophenol, PCP, should not exceed 30 µg/L in raw drinking water (690).

Toxicity Guidelines

The concentration of 2,4-dichlorophenol should not exceed 900 µg/L in raw drinking water (690).

The concentration of 2,4,6-trichlorophenol should not exceed 5 µg/L in raw drinking water (690).

The concentration of 2,3,4,6-tetrachlorophenol should not exceed 100 µg/L in raw drinking water (690).

The concentration of pentachlorophenol should not exceed 60 µg/L in raw drinking water (690).

6.5 Rationale

The reported concentration of 2,3,7,8-TCDD, dioxin, in the Dowicide EC-7 formulation of PCP and in the product currently imported from the US, is <0.05 mg/kg. Thus the concentration of 2,3,7,8-TCDD, the most toxic dioxin, in water containing 30 µg/L of PCP, would not exceed 1.5 picograms/L (1.5 ppq or 1.5 x 10-9 µg/L). This is in the range that EPA is considering setting dioxin discharge limits for pulp and paper mills. In various US states, these limits range from 0.1 to 10.0 ppq, mostly in the 1 to 3 ppq range (403). This is also at or below the range being considered for 2,3,7,8-TCDD in drinking water in BC (692). The PCP guideline would thus protect people from harmful effects due to dioxin contaminants in the PCP, at the known levels of contamination.

The lowest PCP dose having a reported observable effect is 5 mg/kg which is embryotoxic in rats. This is equivalent to about 350 mg/day for the average person. Assuming that this person got all of the daily PCP dose from a daily water intake of 1.5 L, drinking and cooking water would have to reach 240 mg/L of PCP to have such an effect. The lowest LC₅₀ is seven times as great, or 1900 mg/L of PCP in rats and other species (225, 40, 199). If a standard safety factor of 100 was applied to this LC₅₀, then a concentration of about 20 mg/L should not cause any toxic effects, either acute or chronic, in humans. This level is 1000 times higher than the guideline, which is based on taste and odour considerations.

The Health and Welfare Canada levels for chlorophenols are 30 µg/L for PCP, 1 µg/L for 2,3,4,6-TTCP, 2 µg/L for 2,4,6-TCP and 0.3 µg/L for 2,4-DCP (690). These guidelines are met by the group guidelines. If only one isomer was present in a group, and it was present at the guideline level, there could be a slight taste problem for a small number of people. Normally one would expect several isomers to be present at once, and thus no one isomer would reach objectionable levels; however even if such a condition occurred there would be no health hazard due to the safety factor applied at these levels.

The congeners which could cause taste or odour problems at these guidelines levels include 2,3-DCP, 2,3,6-TCP and 2,4,5-TCP; the latter is the only one in commercial use. The major rationale for these guidelines is the fact that they are, or incorporate, the Canadian Drinking Water Quality Guidelines. One must also consider that these are raw water guidelines and that chlorination of water prior to delivery to the consumer may increase the level of chlorophenols to a small extent. In order to minimize such an effect, all raw water should be filtered before it is chlorinated. The reason for the combined chlorophenol guidelines is to accommodate isomer-level testing procedures, which are more economical to carry out, but the levels are set such that even if all the chlorophenol present in an isomer group were the most sensitive isomer, the specific guidelines would still be met.


	Water Quality Ambient Water Quality Guidelines for Chlorophenols 6. DRINKING WATER 6.1 General The major effect of chlorophenols, and PCP in particular, is to uncouple oxidative phosphorylation; this results in inhibition or greatly decreased efficiency in converting ingested food to energy and useful products. This is an essential process in all aerobic organisms, and death will result if the process is stopped. Since the effects on all animals, including people, are essentially the same, and are discussed in Chapter 7 on terrestrial animals they are not repeated here; nor are effects on people singled out and treated separately. Such effects have virtually no bearing on the setting of human drinking water guidelines since organoleptic effects occur at lower concentrations than acute or chronic toxic effects, and such taste and odour effects determine the drinking water guidelines. If one can not taste or smell chlorophenols in the water, there is no health risk and there is also a safety margin over the lowest concentration found to cause a health risk. 6.2 Taste and Odour Chlorophenols are responsible for taste and odour problems in water; such effects are limiting in determining guidelines, since they occur below the LC₅₀ values for organisms (335). The actual guidelines suggested by various agencies for chlorophenols are in the µg/L range, lower than any observed physiological effect level, even after safety factors are applied to the results of taste and odour test panels to allow for more sensitive people in the general population. Tables 6.2.1 and 6.2.2 give some taste and odour thresholds for chlorophenols in water. These tend to be temperature dependent since temperature affects the volatility of chlorophenols. The lowest taste or odour threshold is highlighted in bold type, and given first, for each chlorophenol congener. Taste thresholds tend to be one or two orders-of-magnitude lower than odour thresholds and, since these data are derived using human test panels and water with different characteristics, there is a large amount of variability in the results. 2-MCP, 3-MCP, 4-MCP, 2,4-DCP and 2,4,6-TCP Taste and odour problems in drinking water are reportedly caused by these chlorophenols at very low concentrations in drinking water, in the µg/L range (183, 362, 366, 335, 372), but reference 183 reported little effect by 4-MCP and 2,4,6-TCP at these low levels. 6.3 Literature Guidelines Table 6.3 lists published guidelines for various chlorophenols in drinking water. The most current Canadian guidelines for taste and odour of chlorophenols, by Health and Welfare Canada in 1989 (690), are the same as those in 1987 (110): 30 µg/L for PCP, 1 µg/L for 2,3,4,6-TTCP, 2 µg/L for 2,4,6-TCP and 0.3 µg/L for 2,4-DCP. No guidelines are set for the MCPs. CCME (CCREM) adopted these 1987 Health and Welfare guidelines. The WHO guidelines for 1984 (225) are all 1 µg/L, including 2-MCP and 4-MCP. Taste thresholds appear to be one or two orders-of-magnitude lower than odour thresholds (225). The MCPs are less toxic than their more chlorinated congeners, but there are data to suggest that their taste thresholds could be as low as 0.1 µg/L (335). 6.4 Recommended Guidelines We recommend adoption of the existing Canadian Drinking Water Quality Guidelines for Chlorophenols which have been adopted by the BC Ministry of Health (110, 690), with the addition of a monochlorophenol guideline of 0.1 µg/L (335). The existing Canadian Guidelines only specify specific isomers and omit any mention of others; we have set the guidelines based on the total concentration of all the isomers for each group of chlorophenols. Aesthetic Guidelines (taste and odour) The combined concentrations of all the monochlorophenols, MCPs, should not exceed 0.1 µg/L in raw drinking water (335). The combined concentrations of all the dichlorophenols, DCPs, should not exceed 0.3 µg/L in raw drinking water . The combined concentrations of all the trichlorophenols, TCPs, should not exceed 2 µg/L in raw drinking water . The combined concentrations of all the tetrachlorophenols, TTCPs, should not exceed 1 µg/L in raw drinking water . The concentration of pentachlorophenol, PCP, should not exceed 30 µg/L in raw drinking water (690). Toxicity Guidelines The concentration of 2,4-dichlorophenol should not exceed 900 µg/L in raw drinking water (690). The concentration of 2,4,6-trichlorophenol should not exceed 5 µg/L in raw drinking water (690). The concentration of 2,3,4,6-tetrachlorophenol should not exceed 100 µg/L in raw drinking water (690). The concentration of pentachlorophenol should not exceed 60 µg/L in raw drinking water (690). *6.5 Rationale* The reported concentration of 2,3,7,8-TCDD, dioxin, in the Dowicide EC-7 formulation of PCP and in the product currently imported from the US, is <0.05 mg/kg. Thus the concentration of 2,3,7,8-TCDD, the most toxic dioxin, in water containing 30 µg/L of PCP, would not exceed 1.5 picograms/L (1.5 ppq or 1.5 x 10-9 µg/L). This is in the range that EPA is considering setting dioxin discharge limits for pulp and paper mills. In various US states, these limits range from 0.1 to 10.0 ppq, mostly in the 1 to 3 ppq range (403). This is also at or below the range being considered for 2,3,7,8-TCDD in drinking water in BC (692). The PCP guideline would thus protect people from harmful effects due to dioxin contaminants in the PCP, at the known levels of contamination. The lowest PCP dose having a reported observable effect is 5 mg/kg which is embryotoxic in rats. This is equivalent to about 350 mg/day for the average person. Assuming that this person got all of the daily PCP dose from a daily water intake of 1.5 L, drinking and cooking water would have to reach 240 mg/L of PCP to have such an effect. The lowest LC₅₀ is seven times as great, or 1900 mg/L of PCP in rats and other species (225, 40, 199). If a standard safety factor of 100 was applied to this LC₅₀, then a concentration of about 20 mg/L should not cause any toxic effects, either acute or chronic, in humans. This level is 1000 times higher than the guideline, which is based on taste and odour considerations. The Health and Welfare Canada levels for chlorophenols are 30 µg/L for PCP, 1 µg/L for 2,3,4,6-TTCP, 2 µg/L for 2,4,6-TCP and 0.3 µg/L for 2,4-DCP (690). These guidelines are met by the group guidelines. If only one isomer was present in a group, and it was present at the guideline level, there could be a slight taste problem for a small number of people. Normally one would expect several isomers to be present at once, and thus no one isomer would reach objectionable levels; however even if such a condition occurred there would be no health hazard due to the safety factor applied at these levels. The congeners which could cause taste or odour problems at these guidelines levels include 2,3-DCP, 2,3,6-TCP and 2,4,5-TCP; the latter is the only one in commercial use. The major rationale for these guidelines is the fact that they are, or incorporate, the Canadian Drinking Water Quality Guidelines. One must also consider that these are raw water guidelines and that chlorination of water prior to delivery to the consumer may increase the level of chlorophenols to a small extent. In order to minimize such an effect, all raw water should be filtered before it is chlorinated. The reason for the combined chlorophenol guidelines is to accommodate isomer-level testing procedures, which are more economical to carry out, but the levels are set such that even if all the chlorophenol present in an isomer group were the most sensitive isomer, the specific guidelines would still be met.