A range of organochlorine compounds have been used in Australia for various purposes, including herbicides (e.g., 2,4-D and 2,4,5-T) (Haynes et al. 2000), insecticides (e.g., DDT, lindane, chlordane, dieldrin, aldrin and heptachlor), fungicides (e.g., hexachlorobenzene and chlorinated phenols) and polychlorinated biphenols (PCBs)  (Richardson 1995). Others, such as the dioxins and dibenzofurans, are byproducts of chlorination or combustion processes. Such chemicals enter the marine system via effluents, terrestrial runoff, coastal weed spraying, or other means. Despite the fact that they are internationally recognised as important contaminants in marine environments (Johnson and Ebert 2000), few Australian studies have investigated their local occurrence and distribution (Richardson 1995;  and papers in Hutchings and Haynes 2000). The key properties of organochlorines that cause concern are their toxicity and long-term persistence (Richardson 1995). Organochlorine pesticides are no longer available for use but are still measurable in sediments as a result of their persistence. Another concern is their ability to accumulate in the fatty tissues of living organisms (Phillips 1993). Most studies on organochlorides have focused on their toxicity to and accumulation in mammals and birds and there is relatively little information about their effects on marine invertebrates. This is particularly the case in Australia, where very few studies have been carried out on the effects of organochlorines on native species. Consequently, most knowledge is based on overseas investigations. For instance, herbicides are known to be particularly detrimental to mangroves and seagrasses and adversely affect the animal-algal symbioses in corals, while pesticides interfere with chemical cues responsible for key biological processes, including reproduction and recruitment of a variety of organisms (Peters et al. 1997; Haynes et al. 2000; Prange and Dennison 2000). Other effects relevant to marine invertebrates or their habitats include sublethal effects on crabs as a result of DDT in surrounding waters, and possible effects of DDTs and PCBs on algae (Richardson 1995).

 

Pesticides now in use are generally short-lived organophosphate-type compounds that act quickly and are difficult to detect in the marine environment shortly after application, although they may still cause observable toxic effects. A case in point was azinphosmethyl-contaminated agricultural runoff that entered a South Carolina estuary in 1994. Although this caused significant mortality among juvenile fish and shrimp in a tidal creek, pesticide residues in the water were at or below detection limits within 24 hours of the incident (Chandler et al. 1994;  cited in Engel and Thayer 1998). Some insecticides that target particular processes in insect pests may have similar impacts on marine crustaceans. For instance, the insecticide diflubenzuron (Dimilin®) mimics a juvenile arthropod growth hormone in crustaceans (Christiansen et al. 1978) because it blocks chitin synthesis (Engel and Thayer 1998) and effectively stops the moulting process in juveniles. This finding was important because diflubenzuron was proposed for use to control saltmarsh mosquitos and those same marshes were the prime nursery habitat for many crustaceans (Engel and Thayer 1998). Other investigations have shown that several pesticides, PAHs and metals can be accumulated by blue crabs and cause significant mortalities in laboratory tests, but direct correlations between body accumulation and toxicity for many contaminants is not as clear cut in field situations (Engel and Thayer 1998).

 

Following the restriction of the use of tri-n-butyl tin (TBT) in marine antifouling paints (Section 6.12.4), there has been an increase in the number of formulations containing ‘booster’ herbicides. Scarlett et al. (1999) recorded the occurrence of the antifouling herbicide, Irgarol 1051, within coastal-water seagrasses in 9 out of 10 sites sampled from the east coast of Queensland and within the Great Barrier Reef Marine Park. Although widely distributed throughout European coastal waters, it is not registered in Australia for use as a biocide in antifouling paints. Nonetheless, Scarlett et al. (1999) found concentrations of up to 118 ng g-1 wet weight leaf tissue – the highest plant tissue concentration ever recorded – at one site near the Gold Coast. Such concentrations are potentially toxic and could have consequences for herbivores, seagrass-associated fauna, and the endosymbiotic algae of corals.



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Department of Environment and Heritage