| Summary: | Manganese is a naturally occurring substances that is present in surface waters and biota. Aquatic organisms
have exhibited toxic responses to manganese in surface waters and regulatory bodies in some jurisdictions
have established guidelines for levels of manganese in surface water to protect aquatic life. In British
Columbia, a guideline of 0.1 mg/L was established by the Ministry of Environment, Lands and Parks,
although it was recognized that the scientific data on which this guideline was based were weak. Toxicity
tests applicable to aquatic life in B.C. waters were commissioned to strengthen the relevant data base and to
apply the British Columbia procedures for deriving water quality criteria in an effort to establish more
defensible guidelines for the protection of aquatic life in B.C. Acute and chronic toxicity tests were
conducted on fish, invertebrates and freshwater algae. Acute tests included 48 and 96 hour LC50's, while
chronic tests included reproduction, growth and survival endpoints. A range of organisms was chosen in
order to evaluate the range of sensitivities to manganese.. The possible relationship between water hardness
and toxicity to manganese was also investigated at water hardnesses of 25, 100 and 250 mg/L CaC03.
Data were also gathered from literature sources in support of the new toxicity information. Both acute and
chronic studies were identified for fish species resident in B.C. fresh waters. The collective data were
evaluated for suitability with respect to the B.C. water quality guideline derivation process. Toxicity t test data
that met the requirements for use in guideline derivation were screened for sensitivity in order to fulfill the
objective of developing a guideline protective of the most sensitive aquatic organisms.
A pattern emerged whereby the concentrations of manganese at which adverse effects were observed
increased with increasing water hardness. This pattern was identified in both the literature data and all but
one of the new toxicity tests commissioned by the Ministry of Environment, Lands and Parks. Acute and
chronic regression equations were developed using the most sensitive data for various (in both cases six)
water hardness values. The acute equation was Y = 0.044IX +1.81 and the chronic equation was Y = 0.0176
+ 2.42, where X = water hardness in mg/L CaC03 and Y = Mn concentration in mg/L. The equations were
used to predict manganese concentrations at water hardness increments of 25 mg/L CaC03 over the hardness
range of 25-325 mg/L CaC03, a range that encompasses the vast majority of B.C. surface waters. A factor
of safety of 0.25 was applied to the predicted concentrations to account for uncertainty and was based on
scientific judgement and the strength of the data set used in the derivation process. The resulting acute
manganese concentrations ranged from 0.6 to 3.8 mg/L and are proposed as guidelines for exposure of <96
hours. The resulting chronic manganese concentrations ranged from 0.6 to 1.9 mg/L and are proposed as
guidelines for exposure exceeding 96 hours. While B.C. and other surface water data indicate that
manganese rarely exceeds concentrations of 1 mg/L, it is recognized that natural events may result in periodic
increases. The application of guidelines intended to protect aquatic life from anthropogenic sources of
manganese should reflect this in the sampling methodology requirements.
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