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 BC 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 BC. 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 CaCO3.
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 BC fresh waters. The collective data were evaluated for suitability with respect to the BC water quality guideline derivation process. Toxicity 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 in 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 = 0.0441X + 1.81 and the chronic equation was Y = 0.0176 + 2.42, where X = water hardness in mg/L CaCO3 and Y = Mn concentration in mg/L. The equations were used to predict manganese concentrations at water hardness increments of 25 mg/L CaCO3 over the hardness range of 25-325 mg/L CaCO3, a range that encompasses the vast majority of BC 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 less than 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 BC 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.
ACKNOWLEDGEMENTS
The completion of this thesis research was facilitated by the contribution of several individuals.
I would like to acknowledge the Pacific Environmental Science Centre, Aquatic Toxicity Laboratory, responsible for conducting the aquatic toxicity program. In particular, I wish to thank Mr. Craig Buday and Mr. Scott Steer for their assistance.
I would also like to thank the Water Quality Branch of the B.C. Ministry of Environment, Lands and Parks who commissioned and provided the funding for the toxicity testing program; my sincere thanks to Mr. Les Swain and Dr. Narender Nagpal.
I would like to extend my gratitude to Dr. Sietan Chieng and Dr. Victor Lo of the University of British Columbia, who along with Dr. Nagpal were members of my thesis committee. I gratefully acknowledge the input and guidance provided by Dr. Chieng and Dr. Nagpal, whose efforts were instrumental in the completion of this thesis.
Finally, I wish to acknowledge my family, friends and co-workers for providing encouragement and assistance.