Four of the eight fishing industry sectors have identified pollution as one of the priorities for improvement. Although the pollution types and sources were not further defined, the impacts from persistent organic pollutants are becoming more common worldwide. Toxic effects arising from exposure to chemical pollutants are frequently reported. In addition, contamination by these chemicals can lead to discrimination and/or rejection of the product in the marketplace. The need is for a properly funded study that examines the quality of inshore seawater in a defined area and from which links can be established between cause and effect. For the reasons set out below, the study proposed is seen as Stage 1 of a multi-stage process which will enable the Fishing Industry to understand where it stands currently as far as water pollution by organic chemicals is concerned and the impacts these chemicals might have on specific ecosystem components.
The focus of stage 2 would be to examine the impact of bio-available inorganic chemicals and, separately, increased levels of nutrients on specified key ecosystem components. A subsequent stage could examine the impact of identified industrial chemicals on appropriate indicator species. The aim must be to appreciate the sensitivity of (South) Australian marine ecosystems to pollution from a variety of sources and the impact on market share.
Stage 1.
There is increasing evidence from other States in Australia, and worldwide, that persistent herbicides arising from terrestrial activities are impacting on the growth and productivity of inshore seagrass beds. The toxicity of agricultural chemicals, principally insecticides, has been demonstrated on fish species that are indigenous to the Northern Hemisphere but no study has looked at the toxicity of persistent agricultural chemicals to species found in Australia. And, more importantly, the toxicity of widely used persistent agricultural chemicals to species of commercial importance in South Australia has not been studied.
Recruitment of juveniles from the inshore nursery areas where persistent agricultural chemicals are most likely to be found could be significantly compromised. Modern pesticides, intended for terrestrial use, are toxic at extremely low concentrations.
The levels of persistent herbicides found in marine environments elsewhere in the world are significant, and similar levels would be expected to occur in Australian inshore waters given the extensive use of herbicides in Australian agriculture. The toxicity of persistent herbicides to inter-tidal seagrass species has not been studied in Australia.
A study linking the concentration of a key persistent organic insecticide in the soil, its concentration in the adjacent marine environment and its toxicity to a key marine indicator species such as the prawn, represents a good model for the study of the impact of a non-point source pollutant over a relatively small area.
The contribution by wind-blown topsoil from adjacent farm areas, which can act as a carrier of considerable quantities of adsorbed persistent organic pesticides has not been examined in South Australia. The role of dust-storm events in the transport of toxic chemicals elsewhere in the world is recognised. The concentration in seawater of persistent organic pollutants such as insecticides has not been determined on a seasonal basis.
Dose-response data for a major persistent insecticide and a key indicator marine species such as prawns, combined with knowledge of the concentration of the pesticide in seawater, will provide a scientific basis for proposing modification of land management practices.
The demonstration of significant levels of persistent pesticides in fine farm topsoil and identification of those pesticides in seawater, combined with demonstrated toxicity effects on a key marine species of commercial significance, would provide further support for proposing changes in land-care strategies designed to mitigate these inputs.
