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Risk assessment of chemical mixtures in agricultural landscapes

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  • Chris Holmes
  • Colin David Brown
  • Mick Hamer
  • Russell Jones
  • Lorraine Maltby
  • Eric Silberhorn
  • Jerold Scott Teeter
  • Michael Warne
  • Lennart Weltje


Publication details

JournalEnvironmental Toxicology and Chemistry
DateSubmitted - 30 Apr 2017
DateAccepted/In press - 25 Nov 2017
DateE-pub ahead of print - 28 Nov 2017
DatePublished (current) - 12 Feb 2018
Issue number3
Pages (from-to)674-689
Early online date28/11/17
Original languageEnglish


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.

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