Catherine Neelamraju

Catherine Neelamraju

Catherine Neelamraju is a Senior Scientist in the Queensland Government’€™s Water Quality and Investigations Team (DES) with expertise in assessing interactions across landscapes and conducting water quality risk assessment to inform decision-support frameworks.

Assessing the Ecological Risk of Pesticide Mixtures

Poor water quality has been identified as one of the primary pressures impacting the health and resilience of the Great Barrier Reef ecosystems. In an effort to halt further decline, the State and Federal governments have set water quality targets under the Reef Plan 2050 and the Reef 2050 Water Quality Improvement Plan (WQIP)The pesticide target aims at ensuring aquatic ecosystems are protected. The Water Quality and Investigations team was tasked with developing an ecologically relevant risk assessment metric for the 22 priority herbicides and insecticides identified in the WQIP.

The ms-PAF method is a means of combining the species sensitivity distributions (SSDs) of different chemicals to calculate risk posed by mixtures of chemicals as a fraction or percentage of species that are likely to experience adverse (harmful) effects. Chemicals are first grouped by their modes of action (e.g. photosystem II inhibiting herbicides). The percent of species affected is first calculated within groups using concentration addition, then between groups using response addition.

We used ecotoxological data for species that exist in, or are relevant to, Queensland waterways and estuaries to derive new National Guideline Values. The same data that went into the Guidelines was then used to develop the ms-PAF metric. In this way, we can calculate the percentage of species theoretically affected by the 22 selected pesticides present in each water sample for each site throughout the sampling period, and the resulting data are directly comparable to National Guidelines.

This new risk assessment metric feeds into the Reef and Regional Report Cards, helping decision makers prioritise chemical management under the WQIP. Data-driven decision making is essential if we are to fulfil the primary aim of the WQIP: “Good water quality sustains the Outstanding Universal Value of the Great Barrier Reef, builds resilience, improves ecosystem health and benefits communities”.

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