The persistence of pesticides in atmospheric particulate phase: An emerging air quality issue

Abstract

The persistent organic pollutants (POPs) due to their physicochemical properties can be widely spread all over the globe; as such they represent a serious threat to both humans and wildlife. According to Stockholm convention out of 24 officially recognized POPs, 16 are pesticides. The atmospheric life times of pesticides, up to now were estimated based on their gas-phase reactivity. It has been only speculated that sorption to aerosol particles may increase significantly the half-lives of pesticides in the atmosphere. The results presented here challenge the current view of the half-lives of pesticides in the lower boundary layer of the atmosphere and their impact on air quality and human health. We demonstrate that semivolatile pesticides which are mostly adsorbed on atmospheric aerosol particles are very persistent with respect to the highly reactive hydroxyl radicals (OH) that is the self-cleaning agent of the atmosphere. The half-lives in particulate phase of difenoconazole, tetraconazole, fipronil, oxadiazon, deltamethrin, cyprodinil, permethrin, and pendimethalin are in order of several days and even higher than one month, implying that these pesticides can be transported over long distances, reaching the remote regions all over the world; hence these pesticides shall be further evaluated prior to be confirmed as POPs.

Figure 1. Temporal profile of the normalized concentrations of eight studied pesticides to both OH and O₃ reactivity for an OH concentration of 1.5 · 10⁸ cm⁻³ and 1.7 · 10¹⁴ cm⁻³ of ozone for a period of 6 hours.

Dotted curves represent the exponential fit of the experimental points. The horizontal error bars corresponds to the sampling time of 10 min of particles during the experiment and the error bars of the pesticide concentrations are the standard deviations calculated for three injections of the sample t = 0 h in GC-(QqQ)-MS/MS.

Figure 2. The observed pseudo-first order rate constants in function of OH radical concentrations.

The errors for k^I_{OH (part)} were obtained from the statistical errors of the linear fit. The uncertainties are standard deviations estimated by the Igor Pro software (version 6.3.5.5). The relative OH radical concentration uncertainties were obtained by the sum of the relative uncertainties of mean m-xylene concentrations and rate constant of the reaction between m-xylene and OH radicals (see Eq. S8).

Figure 3. Rate constants estimated by “Atmospheric Oxidation Program (AOPWIN)” of gas phase OH radical reactivity in function of experimental rate constants of heterogeneous OH radical reactivity for number of pesticides.