Iron 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
Iron is the fourth most abundant element in the Earth’s crust and may be present in natural waters in varying quantities depending up on the geology of the area and other chemical components of the waterway (USEPA 1986). The most common oxidisation states of iron in water are the ferrous (Fe2+) and the ferric (Fe3+) states, although other forms may be present in organic and inorganic wastewater streams. In surface waters, iron is generally present in the ferric state; in reducing waters, the ferrous form can persist. The current analytical practical quantitation limit (PQL) for iron is 1 µg/L in fresh water and 2 µg/L in marine water (NSW EPA 2000).
Iron is an essential trace element for both plants and animals, required by most organisms for essential growth and development, and iron deficiency could cause adverse biological effects. However, acute toxicity to aquatic insects has been reported at iron concentrations ranging from 320 to 16,000 µg/L (Warnick & Bell 1969). CCREM (1987) noted that the LC50 for the most sensitive species, the mayfly Ephemerella subvaria appeared anomalous. The 3-week LC50 for Daphnia magna was 5900 µg/L (Biesinger & Christensen 1972). A reduction of 50% in the hatchability of fathead minnow eggs occurred at iron concentrations of 1500 µg/L (Sykora et al. 1972), and the safe concentration for exposure of juvenile brook ranged between 7500 and 12,500 µg/L (CCREM 1987).
In the presence of oxygen, iron is often found as colloidal suspensions of ferric hydroxide, which may remain suspended in water or settled and harden (CCREM 1987). Suspended flocs can cause problems with turbidity, decreased light penetration and smothering of benthic organisms (CCREM 1987, ANZECC 1992).
No adequate data on iron toxicity to saltwater species were available.
There were insufficient data at this stage to derive a reliable trigger value for iron. The current Canadian guideline level is 300 µg/L, which could be used as an interim indicative working level but further data are required to establish a figure appropriate for Australian and New Zealand waters. Potential for iron deficiency needs to be considered in such studies. No marine data were available.
ANZECC 1992. Water quality guidelines for fresh and marine waters. Australian and New Zealand Environment and Conservation Council, Australian Government Publishing Service, Canberra.
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.
Biesinger KE & Christensen GM 1972. Effects of various metals on survival, growth, reproduction and metabolism of Daphnia magna. Journal of the Fisheries Research Board of Canada 29, 1690-1700.
CCREM 1987. Canadian water quality guidelines. Canadian Council of Resource and Environment Ministers, Ontario.
NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.
Sykora JL, Smith EJ, Shapio MA & Synak N 1972. Chronic effect of ferric hydroxide on certain species of aquatic animals. In Proceedings, 4th symposium on coal mine drainage research. Mellon Institute, Pittsburg, Pennsylvania, 347-369. (Cited in ANZECC 1992).
USEPA 1986. Quality criteria for water. US Department of Commerce, National Technical Information Service, US Environmental Protection Agency, Springfield, Virginia. PB87-226759, EPA 440/5 86-001.
Warnick SL & Bell HL 1969. The acute toxicity of some heavy metals to different species of aquatic insects. Journal of the Water Pollution Control Federation 4, 280-284.