Cobalt in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems
Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals' of the ANZECC & ARMCANZ (2000) guidelines.
The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Description of chemical
Cobalt is used in specialised alloys to improve strength and corrosion resistance, such as in aircraft engines or turbines and heavy-duty cutting tools (CCREM 1987). It is also an additive of paint, glass and ceramics (CCREM 1987). Western world consumption of cobalt in 1984 was 17,500 tonnes (CCREM 1987).
Cobalt exists in water most commonly as Co (II) or Co (III), although other forms are possible. It is adsorbed to suspended particles and sediment but its solubility may be increased by complexing with organic matter, such as from sewage works (CCREM 1987). The current analytical practical quantitation limit (PQL) for cobalt is 0.05 µg/L in fresh water and 2 µg/L in marine water (NSW EPA 2000).
Some aquatic organisms may accumulate cobalt, particularly some aquatic plants and benthic organisms (Cole & Carson 1981).
Acute data were available for six species, ranging from 1.1 mg/L (Daphnia magna 48-hour LC50) to 613 mg/L (clawed toad Xenopus laevis 96-h LC50) (CCREM 1987). The lowest geometric mean for D. magna was 1.6 mg/L. The geometric mean for 96-hour LC50 for Pimephales promelas was 10 mg/L.
Screened chronic freshwater toxicity data were available for cobalt for 4 taxonomic groups as follows (pH range was 6.5 to 8.5):
Fish: one species, P. promelas, 210 µg/L (28-day NOEC, growth) to 2740 µg/L (8-day LC50).
Crustaceans: two species, 2.8 µg/L (D. magna; from 28-day NOEC, reproduction) to 790 µg/L (Austropotamoblus pallipes; 30-day LC50).
Algae: one species, 522 µg/L (Chlorella vulgaris, 96-h EC50, population growth).
Although a freshwater moderate reliability trigger value could be derived for cobalt (90 µg/L with 95% protection) using the statistical distribution method, both the 95% and 99% (30 µg/L) figures were well above some experimental chronic figures, particularly for D. magna (between NOEC of 2.8 µg/L and LC50 of 27 µg/L). Hence, a low reliability freshwater trigger value was derived by dividing the lowest chronic figure (2.8 µg/L) by an assessment factor (AF) of 2 (cobalt is an essential element).
Marine chronic data for cobalt comprised 10 data points on eight species from four taxonomic groups, as follows. Figures listed below were converted to NOEC equivalents using the method adapted from van de Plassche et al. (1993).
Marine fish: two species, 4 to 9-day LC50, 52,500 to 227,000 µg/L.
Marine crustaceans: three species, 9-day LC50, 45 µg/L (Palaemon serratus) to 45,400 µg/L (Carcinus maenas). The lowest geometric mean for converted NOEC was 9 µg/L. Homarus vulgaris also had a low geometric mean for NOECs of 65 mg/L.
Marine nematode: one species, Monhystera sp, 4-day LC50, 94,000 µg/L.
Marine algae: two species, 4 to 5-day EC50, growth, 300 µg/L (Dytilum sp.) to 23,600 µg/L (Phaeodactylium sp.).
A marine high reliability trigger value for cobalt of 1 µg/L was calculated using the statistical distribution method at 95% protection.
ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.
CCREM 1987. Canadian water quality guidelines. Canadian Council of Resource and Environment Ministers, Ontario.
Cole CJ & Carson BL 1981. Cobalt in the food chain. In Trace metals in the environment. Vol 6. Cobalt, eds IC Smith & BL Carson, Ann Arbor Science Publications Inc, Ann Arbor, Michigan, 777-924.
NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.
van de Plassche EJ, Polder MD & Canton JH 1993. Derivation of maximum permissible concentrations for several volatile compounds for water and soil. National Institute of Public Health and Environmental Protection, Report 679101 008, Bilthoven, The Netherlands.