Exploring the Toxicity of Secondary Organic Aerosol formed from Atmospheric Oxidation of Pesticides

Global usage of pesticides (all agents that target pests and including insecticides, herbicides, fungicides, and bactericides) was estimated at 4.1 million tonnes of active ingredient in 2015 and is expected to increase by 25% by 2025. Pesticides mainly enter the atmosphere during the spraying application followed by gas-to-particle partitioning, volatisation from surfaces and wind drifting processes. Their atmospheric fate is largely dependent on their physicochemical properties such as their reactivity towards atmospheric oxidants, their vapour pressure dictating their partitioning to particles as well as their potentially significant photolysis rates. Over the past decade, a number of laboratory and field studies have shown that the reaction of current-use pesticides with atmospheric oxidants (such as the hydroxyl radical, OH and ozone, O3) can yield to significant amounts of secondary organic aerosol (SOA) mass. The SOA produced from the oxidation of pesticides can yield products that are potentially more persistent and/or more toxic and can additionally contribute to tropospheric O3 production. Such an increase in the toxicity of the by-products of UV treatment of certain pesticides in water samples has been shown, effected by the UV generation of OH. Similarly, SOA formation from the atmospheric oxidation of pesticides may also increase the toxicity burden. The atmospheric oxidation of organic compounds from biogenic sources have recently found to increase to toxicity burden due to the reactions with OH and O3, and it is reasonable to expect that the SOA formed from the oxidation of the pesticides could affect human and animal health.

We propose to combine cutting-edge, atmospheric simulation chamber (the Manchester Aerosol Chamber, MAC), oxidation flow reactor (OFR) chemistry and cell biology approaches to explore the SOA formation and toxicity from the photo-oxidation of current-use pesticides (i.e. in the presence of OH and O3). The MAC and OFR can provide a controlled environment under atmospherically-relevant environmental conditions that can be used to simulate the atmospheric oxidation of pesticides. Pesticides will be introduced into MAC and OFR by spraying, a process similar to that used in the crops. Subsequently, the lights of the chambers will be switched on, initiating the photochemistry and oxidant production, leading to SOA formation. MAC light sources provide similar actinic flux spectrum to that of the real atmosphere, yet with lower intensity thus resulting to low SOA mass formed. OFR's extensive UV light sources can generate high concentrations of oxidants, yielding high levels of SOA mass that is necessary for the subsequent toxicological assays. State-of-the-science mass spectrometry techniques will be used to benchmark the SOA composition generated from the OFR against those from the MAC, as well as to monitor the physical and chemical properties of the generated SOA. This will further enable the research team to explore their key-properties providing information about their atmospheric lifetimes and fate. The OFR SOA will be sampled in simulated extracellular fluid (SEF) by impingment and aliquots of the samples will be used to assess their cardiac toxicity using a combination of cell lines and intact hearts approaches to evaluate key aspects of cardiac function and markers of dysfunction. Our proposed series of interdisciplinary experiments in our unique facilities will explore our capability to provide information essential to understanding the atmospheric fate, properties and toxicity of SOA generated from the current-use pesticides. Such information is essential in informing policy makers, pesticide manufacturers and users in the development of adequate guidelines and sustainable products. Involvement of project partner Ian Mudway will provide a pathway through to Government via UKHSA through his work on pesticides with the NIHR Health Protection Research Unit.