Poor water quality associated with land-based sediment, nutrient, and pesticide runoff is one of the primary pressures impacting the health and resilience of the Great Barrier Reef (GBR) freshwater and marine ecosystems. The neonicotinoid imidacloprid is detected in an average of 54% of all samples collected annually by the Great Barrier Reef Catchment Loads Monitoring Program, but at up to 100%, of surface water samples in some GBR waterways. This is unsurprising as it registered for, and highly relied upon, in a diverse range of crops including cereals, stone fruit, sugar cane, bananas and various vegetable crops. Other neonicotinoids, such as acetamiprid and clothianidin, are also detected, but far less frequently.
A growing body of literature highlights the potential for neonicotinoid insecticide toxicity to increase over time due to irreversible binding to target receptors within the body of aquatic organisms. If this is the case, the actual ecosystem impact on fresh water and marine (Reef) ecosystems may be greater than that estimated by comparison to default guideline values that are derived using relatively short-term toxicity tests. There may be implications of accounting for cumulative toxicity of neonicotinoid insecticides on the adequacy of current land management and risk mitigation measures for the GBR. This presentation will calculate new proposed ecotoxicity threshold values using toxicity data from longer-term exposures. These will then be used in combination with pesticide concentration data from 28 monitoring sites across 22 unique river basins that drain to the GBR to provide a revised estimate of the risk posed by imidacloprid. As part of this project a new method for including time-cumulative toxicity of neonicotinoid insecticides to calculate ecotoxicity threshold values and in pesticide mixture risk assessment will be presented.