Prospective aquatic risk assessment for chemical mixtures in agricultural landscapes.

Christopher M Holmes,Eric Silberhorn,Lorraine Maltby,Lennart Weltje,Mick Hamer,Colin D Brown,Jerold Scott Teeter,Russell Jones,Leo Posthuma,Michael St J Warne

doi:10.1002/etc.4049

Abstract

Environmental risk assessment of chemical mixtures is challenging because of the multitude of possible combinations that may occur. Aquatic risk from chemical mixtures in an agricultural landscape was evaluated prospectively in 2 exposure scenario case studies: at field scale for a program of 13 plant‐protection products applied annually for 20 yr and at a watershed scale for a mixed land‐use scenario over 30 yr with 12 plant‐protection products and 2 veterinary pharmaceuticals used for beef cattle. Risk quotients were calculated from regulatory exposure models with typical real‐world use patterns and regulatory acceptable concentrations for individual chemicals. The results could differentiate situations when there was concern associated with single chemicals from those when concern was associated with a mixture (based on concentration addition) with no single chemical triggering concern. Potential mixture risk was identified on 0.02 to 7.07% of the total days modeled, depending on the scenario, the taxa, and whether considering acute or chronic risk. Taxa at risk were influenced by receiving water body characteristics along with chemical use profiles and associated properties. The present study demonstrates that a scenario‐based approach can be used to determine whether mixtures of chemicals pose risks over and above any identified using existing approaches for single chemicals, how often and to what magnitude, and ultimately which mixtures (and dominant chemicals) cause greatest concern. Environ Toxicol Chem 2018;37:674–689. © 2017 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Highlights

Many agricultural landscapes contain a mixture of crop types and/or livestock and their management often involves the use of multiple chemicals
16 days were in Maximum Cumulative Ratio (MCR) group I, where an RQ of 1 was exceeded by individual chemicals, out of a total of 63 days where ∑RQ was >1
Regulatory scenarios are developed to provide a pre-specified vulnerability for exposure due to single chemicals (e.g. FOCUS 2001; Fry et al 2014) that is associated with the stated protection goal (e.g. European Food Safety Authority (EFSA) 2013)

Summary

Introduction

Many agricultural landscapes contain a mixture of crop types and/or livestock and their management often involves the use of multiple chemicals. Many of these agrochemicals and veterinary products have the potential to move into and impact aquatic environments, resulting in a potential risk due to exposure to mixtures (Boxall et al 2003; Smith et al 2012; Schreiner et al 2016). Some countries may request the assessment of pesticide tank mixes containing more than one formulated product Beyond these intentional mixtures, applied concurrently in time and space, there is the potential for combined exposure of aquatic environments to multiple chemicals resulting from the combination of land uses, crop types and management practices within catchments (i.e. coincidental mixtures). The potential importance of effects coincidental mixtures is recognized, no specific details are provided on how to assess environmental mixture effects

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