Pervasive pesticide contamination of wetlands in the Great Barrier Reef catchment area

Knowledge of the types and impacts of contaminants occurring in the freshwater wetlands of the Great Barrier Reef catchment area (GBRCA) is limited. The present study examined the presence and concentrations of pesticides occurring in 22 floodplain wetlands, situated in moderate to high-intensity land uses in the GBRCA. The dominant land use within 1 km of the wetlands was sugar cane for 12 wetlands, grazing for 6 wetlands, plantation forestry and conservation for 2 wetlands, and one with an equal mix of land uses. Fifty-nine pesticides and pesticide degradates were detected in the wetlands during 2 consecutive early wet seasons. These included 27 herbicides, 11 herbicide degradates, 11 insecticides, 8 fungicides, 1 nematicide, and 1 pesticide synergist. Each wetland sampled contained between 12 and 30 pesticides with an average of 21 pesticides detected per wetland sampling. Temporal differences existed in the number, types, and average concentrations of pesticides detected. No exceedances of Australian and New Zealand water guideline values were found during the first sampling season, while 10 wetlands had concentrations of at least 1 pesticide exceeding the guidelines during the following sampling season. For 1 wetland, concentrations of 4 pesticides were greater than the prescribed guideline values. Individually, the vast majority of aquatic species would be protected, but in some wetlands, diuron would affect 49% of species and atrazine up to 24% of species. Statistically significant correlations between the number of pesticides and the percentage of intensive land use, primarily sugar cane growing in a 1 km radius of the wetlands, were found. Integr Environ Assess Manag 2020;00:1–15