Risk Assessment of Pesticide Mixtures in Australian Rivers Discharging to the Great Barrier Reef

Abstract

Rivers discharging to the Great Barrier Reef carry complex pesticide mixtures. Here we present a first comprehensive ecotoxicological risk assessment using species sensitivity distributions (SSDs), explore how risk changes with time and land use, and identify the drivers of mixture risks. The analyzed data set comprises 50 different pesticides and pesticide metabolites that were analyzed in 3741 samples from 18 river and creek catchments between 2011 and 2016. Pesticide mixtures were present in 82% of the samples, with a maximum of 23 pesticides and a median of five compounds per sample. Chemical-analytical techniques were insufficiently sensitive for at least seven pesticides (metsulfuronmethyl, terbutryn, imidacloprid, clothianidin, ametryn, prometryn, and thiamethoxam). The classical mixture concepts of concentration addition and independent action were applied to the pesticide SSDs, focusing on environmental threshold values protective for 95% of the species. Both concepts produced almost identical risk estimates. Mixture risk was therefore finally assessed using concentration addition, as the sum of the individual risk quotients. The sum of risk quotients ranges between 0.05 and 122 with a median of 0.66. An ecotoxicological risk (i.e., a sum of individual risk quotients exceeding 1) was indicated in 38.5% of the samples. Sixteen compounds accounted for 99% of the risk, with diuron, imidacloprid, atrazine, metolachlor, and hexazinone being the most important risk drivers. Analysis of land-use patterns in catchment areas showed an association between sugar cane farming and elevated risk levels, driven by the presence of diuron.

Interactions among multiple stressors vary with exposure duration and biological response

“…Increased turbidity due to elevated total suspended sediments alongside increased phytoplankton biomass as a result of eutrophication cause a decrease in the amount of photosynthetically active radiation available to aquatic photosynthetic organisms such as seagrasses, macroalgae and microalgae [25–27]. Diuron, a PSII-inhibiting herbicide, was chosen based on Queensland catchment and marine monitoring data adjacent to the Great Barrier Reef (GBR) [20,28–31] that indicates it is one of the most frequently detected pesticides year-round in waters entering the GBR [32,33].…”

“…Increased turbidity due to elevated total suspended sediments alongside increased phytoplankton biomass as a result of eutrophication cause a decrease in the amount of photosynthetically active radiation available to aquatic photosynthetic organisms such as seagrasses, macroalgae and microalgae [25][26][27]. Diuron, a PSII-inhibiting herbicide, was chosen based on Queensland catchment and marine monitoring data adjacent to the Great Barrier Reef (GBR) [20,[28][29][30][31] that indicates it is one of the most frequently detected pesticides year-round in waters entering the GBR [32,33]. The aims of this research were (i) to predict the nonlinear effects of diuron exposure, DIN enrichment and reduced light on two response variables, photosynthesis and growth; (ii) to identify how interaction types for the two response variables vary over different exposure durations; and (iii) to compare the interaction types for the two response variables at the same experimental treatment levels.…”

Pervasive Pesticide Contamination of Wetlands in the Great Barrier Reef Catchment Area

“…Herbicides and other pesticides are known to dominate contaminant mixtures found in river systems influenced by agricultural areas (Brodie et al 2015; Devlin et al 2015; Rasmussen et al 2015; Schreiner et al 2016; Bartley et al 2017; Szöcs et al 2017; Lambropoulou et al 2018; Spilsbury 2018; Warne et al 2020). Spilsbury (2018) analyzed 3757 grab samples from the Great Barrier Reef Catchments Loads Monitoring Program (Huggins et al 2018) and found the number of different pesticides detected (i.e., concentrations were greater than the chemical's LOR in each sample varied from 0–23).…”

Colloidal silica nanomaterials reduce the toxicity of pesticides to algae, depending on charge and surface area

“…[7][8][9] They can also be used to carry pesticides and release them in a controlled way, reducing the total amount of pesticide that needs to be applied and thereby reduce adverse impacts on non-target organisms. 10,11 The wide and large use of pesticides is currently causing a significant risk to the aquatic environments (both autotrophs and heterotrophs species) [12][13][14] and measures for reducing their concentrations in waters are therefore coveted. 15,16 Silica NMs (or nanocomposites containing silica) are particularly suitable for use in applications mentioned above because of their facile preparation and a number of unique properties, including thermal stability, mechanical strength, tunable structure (shape and porosity), biocompatibility and a surface allowing functional modifications.…”