State of the Environment Report 2007
Contamination of inland waters usually results from contamination of land (see 'Land contamination'). The number of contaminated inland waters is currently difficult to ascertain, but is usually associated with identified land contaminated sites. Unsafe storage, use or disposal of chemicals in the industrial, business, agriculture or urban environment is the major cause of contamination of inland waters. This may be exacerbated by poor waste treatment or management practices. Waste by-products (such as paints, oil, solvents or chemical residues) dumped into drains because it is a cheaper and easier way to dispose of them, may form dangerous chemical cocktails that can be environmentally damaging and harmful to human health. Clean-up can be especially difficult, costly and may result in offenders being prosecuted. A survey of 522 light industries adjacent to the Swan-Canning rivers showed wastewater containing chemicals and pesticides was disposed of through soakage into soil (19%), stormwater drains (16%), septic tanks (13%) and sewers (Swan River Trust, 1999). About 50% of industrial premises did not undertake wastewater treatment and less than 5% conducted periodical testing and maintenance of their treatment facilities. Many light industries did not understand the potential contamination risk or best practices for industrial wastewater management.
Persistent chemicals that are mobile in water (such as pesticides, herbicides and organic chemicals) pose the greatest risk to aquatic flora and fauna. It is currently estimated that 11% of major fish kills can be attributed to contamination of inland waters (T Rose, Department of Environment, pers. comm.). The effect of some contaminants is increased by their ability to persist and build up in the environment over time. This can be particularly destructive for wetlands, river pools and some estuarine systems where flushing is limited. In 1997, a major fish kill occurred in an Ord River irrigation channel and the Dunham River due to pesticide (Endosulfan) contamination. Current pesticide practices have changed profoundly since the early stages of the Ord Irrigation Scheme (1960s), where highly toxic and persistent pesticides were used. However, recent sampling indicates that some pesticides persist in local fish and animals (Department of Environment, unpublished). Another pesticide spill at a racecourse in 1997 in the Swan River near Perth caused major fish death, killing over 30% of the river's bream fish stock.
In Perth, groundwater quality is generally good but there are areas where contaminants have affected shallow groundwater. In particular, leaking underground storage tanks at petrol stations are a widespread threat to groundwater, due to their large number and distribution. Leaks may go undetected for long periods and, on reaching groundwater, contaminants may affect drinking water supplies, residential or production bores, and eventually wetlands and waterways. Of about 6500 licensed premises in WA with dangerous goods, an estimated 57% have underground storage tanks. Nearly half of these are located in the Perth metropolitan area. Just over 3% (or 217) of premises have leaking tanks and many of the sites involved are being investigated and undergoing remediation.
Recent monitoring of heavy metals, pesticides and other toxicants in inland waters is limited. Occasional sampling of toxicants from stormwater drains discharging to the Swan and Canning rivers show some have elevated organic chemicals, pesticides (including DDT and Dieldrin), hydrocarbons and heavy metals such as chromium, cadmium copper, lead and zinc (Wong & Morrison, 1994; Department of Environmental Protection, 2001; Swan River Trust, 2003a & 2003b). Although the more persistent and toxic pesticides are now banned (e.g. DDT), it is possible that a gradual release of contaminants to wetlands and waterways is occurring via slow moving groundwater plumes. Monitoring in the City of Stirling and some parts of the Gnangara Mound showed some bores are contaminated with arsenic, aluminium and other heavy metals in response to acidification events (Appleyard, 2004 & 2005). Sampling of deep drains in the agricultural Wheatbelt has also shown high levels of heavy metals including iron, aluminium, cobalt, copper, zinc, lead and uranium have leached under acidic conditions (Rogers & George, 2005). Similarly, heavy metals have been found in some inland waters following acid mine drainage and where acid sulfate soils are found.
The economic costs of inland water contamination are considerable and far outweigh the substantial cost of remediation efforts. Property values may decline, fisheries may be impacted, and recreation and tourism can be detrimentally affected. If the contamination occurs in a water supply it may restrict virtually all forms of water use. Discovery of a contaminated wetland or waterway close to residential areas may cause considerable community concern and distress, irrespective of the risk of potential exposure to the contaminant. It may also present a threat to social or cultural values. Humans may also be at risk if exposed through contaminated drinking water or eating affected fish, livestock or other affected produce.
