The strategy used to derive a water quality guideline for sulphate to protect aquatic life was to assess the available aquatic toxicological data for sodium sulphate, magnesium sulphate and potassium sulphate which are soluble in water, and for calcium sulphate which is relatively insoluble. These compounds were chosen for assessment because of the innocuous nature of the cations, Na, Mg, K, and Ca, and their common occurrence in natural waters. The purpose of this assessment was to derive a guideline for SO4 without masking by more toxic substances such as the copper in CuSO4, or from acidity as in the case of sulphuric acid (H2SO4). In such cases the water quality guidelines for the more toxic copper or acidity should apply, and such data were not used in this assessment. However, the possibility of some toxic influence from the presence of the added cations (Na, Mg, K, and Ca) cannot be excluded.
Initially, the available toxicological data was screened for exotic species that should be excluded from the assessment such as brine shrimp (Artemia salina), bleak (Alburnus alburnus) and the harpacticoid copepod (Nitocra spinipes) which are brackish water inhabitants. While some species included in the data set are not indigenous to British Columbia waters, they were included as indicator species, to represent related taxonomic groups that may live in BC, but for which no data were available. The toxicity data for freshwater organisms were downloaded from the US EPA on-line aquatic toxicological data base AQUIRE, as well as data from other sources. These data are summarized in Table 2 and converted from µg/L or molar Na2SO4, MgSO4, K2SO4, and CaSO4 to mg/L SO4 to ensure that the data are comparable. On reviewing original key references, numerous data points in the AQUIRE database were found to be incorrect. The incorrect values were identified and replaced with the correct data from the original references where appropriate in Table 2.
Effect values >10 000 mg/L were deleted from the data set because, to derive a water quality criterion to protect aquatic life, the lower effect levels are the most critical.
The tabulated data were screened for the more sensitive effect levels (below 1000 mg/L SO4) and the original published studies were assessed to determine if they were appropriate to derive a guideline (i.e., no unusual confounding factors such as heavy metals or pH ranges outside normal ambient levels, etc.) and if they were based on good science. These decisions are, in part, subjective but follow the principles specified in the draft "Derivation of Water Quality Guidelines to Protect Aquatic Life in British Columbia" (Water Quality Branch, 1995).
The following discussions for freshwater aquatic life will focus on the studies shown in Table 2 with harmful effect levels < 1000 mg/L SO4.
A discussion of the toxicity of sulphate to marine life was omitted from this section and a guideline for sea water was deemed unnecessary because of the high levels of sulphate typically present in sea water (see Section 3.3.2 ). In addition, there was a paucity of information on the toxic effects of sulphate to marine organisms.
Effects on Algae
Freshwater Algae
Based on experiments in an early study performed by Beauchamp (1954), McKee and Wolf (1963) reported that water containing < 0.5 mg/L sulphate will not support the growth of algae. The State of Kentucky also recognizes that sulphur is an essential plant nutient and that sulphate in excess of 0.5 mg/L is essential for algal growth (Kentucky Water Watch web site).
The lowest value of SO4 in Table 2 that was reported toxic to phytoplankton (4 mg/L SO4) by Jayaraj et al. (1992) was rejected from this assessment because the toxicity tests were designed to test for the ameliorative effects of calcium, magnesium and iron on copper, cadmium and nickel toxicity. The magnesium was added as MgSO4.
The blue-green algae Anabaena was reported to undergo early sporulation when reared in sulphate-supplemented media at concentrations of 216 and 311 mg/L (as SO4) according to Kanta and Sarma (1980).
The AQUIRE database reported effect levels of sodium sulphate on two algae species (Microcystis aeruginosa and Selenastrum capricornutum) from a study by Yamane et al. (1982). A review of the original report revealed that the compound tested was alkyl sulphate, not sodium sulphate. This data was rejected as a basis to derive a water quality guideline for sulphate because of potential interference of the alkyl group.
Bioassays performed for BC Ministry of Environment, Lands and Parks (MELP) at the Pacific Environmental Science Centre (PESC) using the freshwater algae Selenastrum capricornutum determined an IC50 for growth of 1868 mg/L SO4 and a Lowest Observed Effect Concentration (LOEC) and No Lowest Observed Effect Concentration (NOEC) of 1111 and 370.4 mg/L, respectively. Deionized water was used as the diluent in the test which would not represent ambient conditions. (Unpublished BC MELP data, 1996).
BC Research Inc.(1998) performed a series of spiked sulphate laboratory bioassays to assess the impact of simulated mine plant effluent with elevated sulphate levels on aquatic organisms. Included in this suite of bioassays was a 72-h algal growth inhibition test using Selanastrum capricornutum exposed to the simulated effluent spiked with Na2SO4. A NOEC and LOEC of 1060 and 3650 mg/L SO4, respectively, were reported. Also, an IC25 and IC50 for growth inhibition of 2210 and 3359 mg/L SO4, respectively, were reported.
Effects on Aquatic Macrophytes
Aquatic mosses appear to be the most sensitive freshwater organisms to sulphate that were identified in this review. The AQUIRE database transcribed data incorrectly from a study by Frahm (1975). AQUIRE reported mortality to four species of aquatic moss, Fontinalis antipyretica, Fissendens crassipes, Leptodictum riparium, and Leskea polycarpa at concentrations of 100 mg/L, 150 mg/L, >200 mg/L and >200 mg/L as K2SO4, respectively, after a one-week exposure. However, the original publication by Frahm (1975) reported these values measured as SO4, not K2SO4, so conversions were unnecessary and the data reported accordingly. At least one species tested, Fontinalis antipyretica, is known to be widely distributed throughout BC, especially near the coast and in the lower pH waters.
To challenge the scientific reliability of the aquatic moss toxicity data reported by Frahm (1975), Beak International Incorporated, together with Michigan Technological University (1998) performed 14-day bioassays on the aquatic moss, Fontinalis neomexicana, exposed to sodium sulphate concentrations up to 500 mg/L (as SO4) at water hardness of 160 mg/L (as CaCO3). The responses measured were chlorophyll a and b content. Based on their observations, they concluded that sulphate concentrations up to 500 mg/L would not be harmful to aquatic life in hard water conditions such as those tested here. However, in-house plant specialists (P. Warrington and R. Nordin, personal communication) expressed some concern as to the merits of monitoring chlorophyll a and b content as a measure of moss health. The measurement of chlorophyll a and b content is really a surrogate measure of plant biomass and since aquatic mosses grow very slowly, such a measurement may be a poor indicator of the relatively short-term viability of moss populations exposed to sulphate. It was considered doubtful that chlorophyll a and b content in moss cuttings would change much under the test conditions. While chlorophyll content is fairly easy to measure, photosynthetic impairment, or a test designed to measure impairment of the naked free-swimming sperm would be a far better measure of plant health, and of its ability to maintain a viable population in a stream system.
Stanley (1974) measured the effects of a number of compounds including Na2SO4 on the growth of Eurasian watermilfoil (Myriophyllum spicatum L.) over 32 days of exposure. Transposed effect values to the AQUIRE database appear to be incorrect. Corrected 32-d EC50's for root and stem growth ranged from 2785 to 7011 mg/L (as SO4). The sodium may have been the active ingredient affecting turgor pressure. Lower concentrations of Na2SO4 stimulated growth.
Effects on Invertebrates
Freshwater Invertebrates
Acute Toxicity
Fisher et al. (1991) determined a 1-d LC50 of 112 mg/L for zebra mussels (Dreissena polymorphia) of 62 mg/L (as SO4) exposed to K2SO4 as shown in Table 2. However, through a series of toxicity tests using potassium compounds, Fisher et al. (1991) concluded that the potassium (K+ ion) was the toxic moiety of the compound to the zebra mussels, not the sulphate. This data was rejected as a basis to derive the sulphate water quality guideline because the sulphate did not cause the toxicity reported.
Effect levels of sodium and magnesium sulphate on amphipods (Hyallela sp.), mosquito larvae (Culex sp.), cladocerans (Daphnia magna), and pond snail eggs (Lymnaea sp.) cited from Dowden and Bennett (1965). These values appear to have been incorrectly transcribed from the original reference to the AQUIRE database. The results have been re-entered correctly to Table 2. The corrected 1- to 4-d LC50's for the amphipods exposed to Na2SO4 ranged from 595 to 1609 mg/L (as SO4) The 1- and 2-d LC50 for the mosquito larvae exposed to Na2SO4 are 7727 and 9025 mg/L (as SO4). The 1- to 4-d LC50 for Daphnia magna exposed to Na2SO4 and MgSO4 ranged from 426 to 5668 mg/L (as SO4). Corrected values for reduced hatching success of Lymnaea eggs exposed to Na2SO4 and MgSO4 for 1- to 4-days ranged from 2402 to 8403 mg/L (as SO4).
The AQUIRE database reported 1- and 2-d EC50's of 406 and 344 mg/L for Daphnia magna exposed to MgSO4 from a study by Khangarot and Kay (1989). The concentrations in the original reference were reported as the Mg2+ ion concentration. Similarily, in a separate study by Khangarot (1991), the toxicity of Mg2+ ions were tested on tubificid worms (Tubifex tubifex) but the values transcribed to the AQUIRE database were reported as the Mg2+ ion concentration. Hence, the data were not appropriate to serve as a basis for the derivation of sulphate water quality guidelines.
Fairchild (1955) reported that the threshold toxicity concentration of sodium sulphate toward Daphnia depended on the dissolved oxygen (DO) concentration. At a DO concentration of 6.6 mg/L, the toxicity threshold of Na2SO4 was 5514 mg/L; but at a DO concentration of 1.46 mg/L, the toxicity threshold of Na2SO4 dropped to 2752 mg/L.
BC MELP had The Pacific Environmental Science Centre (PESC) perform a series of acute toxicity bioassays using the freshwater invertebrates Daphnia, Hyalella, and Chironomids exposed to SO4 under three different water hardnesses, 25, 100, and 250 mg/L (as CaCO3). Generally, for most aquatic organisms tested including fish, toxicity decreased with increased water hardness. Chironomids were the only organisms that showed the opposite trend (Figure 3). Reported 48-h LC50s for Daphnia in soft water (hardness of 25 mg/L as CaCO3), well water (hardness of 100 mg/L), and hard water (hardness of 250 mg/L), were 537, 6281, and 7442 mg/L SO4, respectively. For Hyalella, reported 96-h LC50s in the soft, medium and hard water were 205, 3711, and 6787 mg/L, respectively. Chironomids appeared considerably less sensitive to SO4 in soft water than the other invertebrates tested, where 96-h LC50s in the soft, medium, and hard water were 6667, 5868, and 4173 mg/L, respectively. (Unpublished PESC data, 1996). The hypersensitivity of Hyalella to sulphate demonstrated in the series of PESC bioassays conflicts with information cited by Beak (1997b), where Hyalella azteca is reported as one of a few freshwater organisms that thrives in saline prairie lakes containing 30 000 mg/L of dissolved salts, of which MgSO4 is typically the dominant salt species. The reason for this discrepancy is not known but may be linked to the soft water used in the key PESC data or the acclimation of species over time.
As noted in Section 5.1.1, BC Research Inc.(1998) performed a series of spiked sulphate laboratory bioassays to assess the impact of elevated sulphate levels on aquatic organisms. Included in this suite of bioassays were a 48-h acute toxicity test using the cladoceran, Daphnia magna, and a 96-h survival test using the amphipod Hyalella azteca. Water hardness of the test solutions ranged from about 105 to 116 mg/L (as CaCO3). For Daphnia, a NOEC and LOEC of 3650 and 7460 mg/L SO4, respectively, and a 48-h LC50 of 5218 mg/L SO4, was reported. For Hyalella, a NOEC and LOEC of 1060 and 3650 mg/L SO4, respectively, were reported and, a 96-h LC50 of 1226 mg/L SO4 was also determined.
Chronic Toxicity
To assess the chronic effects of elevated sulphate concentrations emanating from a Vancouver Island coal mine, Denisger (1997 draft) reported on chronic Daphnia bioassays performed at the Pacific Environmental Science Centre (PESC) using on-site water collected downstream from the mine. Control water for the test was laboratory source water from the Capilano River. Effects studied included reproductive success, survival time to first brood, and growth or mobility inhibition. Four of six site waters tested showed no environmental effects for Daphnia after chronic exposure however, reproduction and survival effects at one of the sites could not be explained by differences in water quality, and toxicity at the other site was thought possibly to be due to hydrogen sulphide detected in the test water. The highest dissolved sulphate concentration used in the Daphnia laboratory bioassays was 420 mg/L from settling pond and coal wash plant drainage. No significant difference in effects was noted for Daphnia between this test water and the control.
BC MELP requisitioned PESC to conduct 21-day chronic Daphnia bioassays to assess the toxicity of SO4 in water of hardness 100 mg/L and 250 mg/L (as CaCO3). No chronic Daphnia tests were performed in the soft water (25 mg/L as CaCO3) because Daphnia typically do not survive well in soft water. A LOEC, NOEC, and an IC25 (25% inhibition of reproduction) of 1200, 625, and 833 mg/L SO4, respectively were reported for medium water hardness. In hard water, a LOEC, NOEC, and an IC25 of 1375, 795, and 1476 mg/L SO4 were reported (Unpublished PESC data, 1996).
As noted in Section 5.1.1, BC Research Inc.(1998) performed a series of spiked sulphate laboratory bioassays to assess elevated sulphate levels. Included in this suite of bioassays was a 7-day survival test using the cladoceran , Ceriodaphnia. A NOEC and LOEC of 1060 and 3650 mg/L SO4, respectively, were reported. A 7-day IC25 and IC50 for reproduction of 1267 and 2061 mg/L SO4, respectively, were reported, as well as a 7-day LC50 of 1355 mg/L SO4.
Effects on Fish
Freshwater Fish
Acute Toxicity
The lowest toxic values to freshwater fish reported in the AQUIRE aquatic toxicological database were 15 and 22 mg/L (converted to SO4) after five days of exposure. However, the original published study (Horn et al. (1949) from which these data were derived reported only one minimum lethal concentration of 100 mg/L Na2SO4 (equivalent to 67.6 mg/L SO4). This value was based on a screening test using one to five emerald shiners (Notropis atherinoides). The AQUIRE reference relied upon author communication for the data reported. In view of the publication date of this study (1949), reliable confirmation of these reported values is unlikely. In addition, according to the original reference, only one fish may have been used in the test and no control tests were reported. In view of these factors, the values reported in this study were rejected as a basis to derive a water quality guideline for sulphate.
The AQUIRE database reported several LC50 values ranging from 55 to 744 mg/L for Na2SO4 (converted to SO4 by this author) on striped bass (Morone saxatilus) by Hughes (1973) that were cited from a secondary reference. These secondarily reported data in the AQUIRE database do not agree with the original published data and therefore were rejected by this author. The original data from Hughes (1973) has been added to Table 2 directly below the rejected data. These corrected 1 to 4-day LC50's ranged from 2000 to 250 mg/L SO4 , respectively for striped bass larvae. The 4-day LC50 of 250 mg/L SO4 for Morone saxatilus larvae was the lowest (most toxic), reliable toxic concentration reported in the literature reviewed for fish. The lowest LC0 (no mortality) for this species was 100 mg/L after four days of exposure. One to 4-day LC50's reported for striped bass fingerlings were all 3500 mg/L and the LC0 for all exposure durations (1- to 4-day) was 2500 mg/L. While this particular species of bass is not resident in British Columbia, this species serves as an indicator for bass (largemouth and smallmouth bass) and perch (yellow perch) species that are indigenous to BC but for which no toxicological data exists.
The AQUIRE database reported several effect levels of sodium and magnesium sulphate on bluegills (Lepomis macrochirus) and gobbies (M. latipinna) cited from Dowden and Bennett (1965). These values appear to have been incorrectly transcribed from the original reference to the AQUIRE database and have now been re-entered correctly to Table 2. The corrected 1-d LC50's for exposure of Lepomis macrochirus to Na2SO4 and MgSO4 are 11 831 and 15 162 mg/L (as SO4). The corrected 1- and 2-d LC50's for exposure of M. latipinna to Na2SO4 are 11 831 and 13 548 mg/L (as SO4).
Wallen et al. (1957) tested the toxicities of Na2SO4, MgSO4 and CaSO4 separately to the mosquito fish (Gambusia affinis) in the presence of high turbidity (measured with a Jackson turbidimeter but results reported as ppm?) which ranged from between 3000 mg/L at the onset of the tests to <25 mg/L at the end to simulate turbid water conditions in Oklahoma. The results tabulated in the AQUIRE database appear to have been incorrectly transcribed from the original reference. The corrected data was entered into Table 2. One to 6-d LC50 concentrations for Na2SO4, MgSO4 and CaSO4 ranged from 6761 to 44 688 mg/L (as SO4). The highly turbid diluent water used in the tests disqualify the results as a basis for a water quality guideline for BC waters.
Tsuji et al. (1985) reported 1- and 2-d LC50's of >1000 mg/L for killifish (Oryzias latipes) exposed to MgSO4 at three temperatures (10, 20 and 30°C). These concentrations were reported as the metal concentration (Mg), not MgSO4 as reported in the AQUIRE database. Hence, these data are not suitable as a basis to derive a water quality guideline for sulphate.
Boge et al. (1982a,b) studied the effects of sulphate ions on enzymatic activities in the gut and gill of the European eel (Anguilla anguilla) under constant temperature conditions and when exposed to heat shock. Changes in enzyme activity were noted under both temperature regimes when exposed to 176 mg/L SO4, when applied as K2SO4 and CaSO4. This concentration includes the sulphate concentration of the diluent which already contained 76 mg/L SO4. While biochemical changes were noted, these may be an adaptive response and may not result in detrimental physiological effects. The European eel is not indigenous to British Columbia.
Boge et al. (1982c,d) performed identical studies on enzymatic activity using rainbow trout (Oncorhynchus mykiss) in place of eels. No changes were noted when exposed to the same sulphate concentration (176 mg/L as SO4) and under the same temperature regimes as the eels.
BC MELP contracted PESC to perform a series of acute toxicity bioassays using rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) exposed to SO4 under different water hardness conditions. Generally, for most aquatic organisms tested including fish, toxicity decreased with increased water hardness. The 96-h LC50s for rainbow trout in soft water (hardness of 25 mg/L as CaCO3), well water (hardness of 100 mg/L), and hard water (hardness of 250 mg/L), were 5000, 9750, and 9900 mg/L SO4, respectively. For coho salmon, 96-h LC50s for the soft, medium, and hard water were 5742, 9550, and 9875 mg/L, respectively (Unpublished BC MELP data, 1996).
Chronic Toxicity
To assess the chronic effects of elevated sulphate concentrations emanating from a coal mine, Denisger (1997 draft) performed in-situ chronic coho salmon (Oncorhynchus kisutch) egg bioassays in the Quinsam River watershed near Nanaimo, BC. An intensive water quality monitoring program was conducted in conjunction with the bioassays. Four test sites and one control site were chosen for the study. The site with the highest dissolved sulphate concentration (drainage from the settling pond and coal wash plant) ranged from 281 to 1111 mg/L. Coho egg mortality of 20% was reported at this site. The author suggested that the predominant factor affecting toxicity of the coho eggs at this site may have been the elevated sulphate levels. A sample of this same site water was used to test Daphnia in the laboratory (sulphate concentration of 420 mg/L) but showed no significant toxicity over the control water (see Section 6.3.1).
Beak International Incorp. (1997b) has reported field observations from sulphate-enriched waters near three separate minesites in Ontario, Quebec, and New Brunswick. At the Quebec site (Beak, 1996a), salmon survival was reportedly unimpaired at sulphate concentrations of 45 to 160 mg/L in spring and from 180 to 300 mg/L in fall. Similarly, at the New Brunswick minesite (Beak, 1997a), benthic and fish communities were reportedly unimpaired at sulphate concentrations which ranged from 170 to 250 mg/L. Any harmful effects noted in exposed aquatic organisms during these field observations were attributed to substances other than sulphate, such as metals or ammonia. Assessment of the relevance of sulphate toxicity from such field observations is often difficult due to the uncontrolled influence of confounding factors.
BC MELP had the Pacific Environmental Science Centre (PESC) perform 7-day early life stage (e-test) rainbow trout bioassays exposed to SO4 under different water hardness conditions. Reported 7-day EC50's for the young rainbow trout in soft water (hardness of 25 mg/L as CaCO3), well water (hardness of 100 mg/L), and hard water (hardness = 250 mg/L), were 1105, 1025, and 3116 mg/L SO4, respectively (Unpublished BC MELP data, 1996).
As noted in Section 5.1.1, BC Research Inc.(1998) performed a series of spiked sulphate laboratory bioassays to assess elevated sulphate levels on aquatic organisms. Included in this suite of bioassays were a 7-day salmonid embryo viability test (e-test) using the rainbow trout, Onchorhynchus mykiss, and a 7-day survival and growth test using the fathead minnow Pimephales promelas. For rainbow trout embryo viability, a NOEC and LOEC of 1060 and 3500 mg/L SO4, respectively, were reported. A 7-day EC25 and EC50 for viability of 1280 and 1477 mg/L SO4, respectively, were also reported for the trout embryos. For the fathead minnow test, a NOEC and LOEC for survival of 510 and 1060 mg/L SO4, respectively, were reported, and for growth, a NOEC and LOEC of 1060 and 3650 mg/L SO4, respectively, were reported. Also, an IC25 and IC50 for growth of 2255 and 3450 mg/L SO4, respectively, were determined, as well as a 7-day LC50 of 1355 mg/L SO4.
In an earlier publication McKee and Wolf (1963) reported that of good game fish waters in the US, five percent of these waters contain <11 mg/L sulphates, 50 % <32 mg/L, and 95 % < 90 mg/L.
Guidelines From the Literature
A provisional water quality objective of 100 mg/L maximum for sulphate was set for the Yakoun River and its tributaries to protect aquatic life (Nijman, 1993). This objective was based on toxicity studies using eels (Anguilla anguilla) and fish (striped bass Morone saxatilus) that are not resident in BC waters (see Section 6.5.1).
A Provisional water quality objective for sulphate of 50 mg/L average concentration (five samples in 30 days) was set for Cahill Creek, Nickel Plate Mine Creek, and Red Top Gulch Creek in the Okanagan area of BC (Swain, 1987). The rationale behind this objective is that, according to Beatty, (personal communication), above an average concentration of 71 mg/L sulphate (range of 27.7 to 189 mg/L) large sulphur bacteria growths can cover creek beds and result in significant changes to the macroinvertebrate community. However, at another location in the Okanagan area, despite sulphate concentrations which have averaged between 150 to 450 mg/L for about the past decade, no dense growths of sulphate bacteria have been observed (J. E. Bryan, personal communication).
Recommended Guideline
Freshwater Aquatic Life
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.
Since there is conflicting evidence over the sensitivity of aquatic mosses to sulphate it is recommended that for impacted waterbodies with concentrations of dissolved sulphate that exceed 50 mg/L, the health of aquatic moss populations should be checked on an occasional basis.
Rationale
The guideline is based primarily on three studies which investigated the effects of sulphate on freshwater organisms. These are as follows:
i. Hughes (1973) reported 1-, 2-, 3-, and 4-d LC50's of 2000, 1000, 500, and 250 mg/L for SO4, and LC0's (no effect) of 500, 100, 100, and 100 mg/L, respectively, for striped bass (Morone saxitilus) larvae.
ii. Unpublished data from a series of toxicity tests performed by The Pacific Environmental Science Centre (PESC) for BC MELP in 1996 showed that the amphipod, Hyalella, was sensitive to sulphate in soft water, but not in medium (100 mg/L as CaCO3) to hard water (250 mg/L as CaCO3). PESC reported 96-h LC50s for Hyalella in soft, medium and hard water of 205, 3711, and 6787 mg/L SO4, respectively. A water quality guideline of 100 mg/L provides protection with a 2:1 safety factor in soft water, and a significantly greater safety factor in harder water more typical throughout BC.
iii. Frahm (1975) demonstated that a concentation of 100 mg/L SO4 was toxic to the aquatic moss, Fontinalis antipyretica, a species which is known to be widely distributed throughout BC. Toxicity of SO4 to four other species of aquatic moss ranged from 100 to >250 mg/L. There are more recent data (Beak International Incorporated and Michigan Technological University, 1998) that conflicts with these earlier (Frahm, 1975) data but the chosen endpoint of the newer data is in question.
iv. There is some evidence that elevated sulphate levels (average of 71 mg/L sulphate; range of 27.7 to 189 mg/L) can stimulate large sulphur bacteria growths which can cover creek beds and result in significant changes to the macroinvertebrate community. Anecdotal evidence is not used to derive water quality guidelines due to the absence of scientific defensibility of such information. But such information is worth noting to provide the impetus to stimulate the necessary future research into such observations.
Application of Guideline
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 Environment publication, "Methods for Deriving Site-Specific Water Quality Objectives in British Columbia and Yukon" should be followed.