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).
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
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.