Transformations of Pesticides in the Atmosphere: A State of the Art

The current knowledge about transformation rates and products of pesticides in the atmosphere is reviewed. Reactive species and their concentrations in the atmosphere are presented. Reactions of pesticides with these species (including photolysis) in the gas and the particulate phase are evaluated from available experimental data. The potential of estimation methods is discussed. Experimental techniques for laboratory and outdoor measurements are reviewed. Finally, an estimation is made of uncertainties in atmospheric lifetimes due to chemical or physical reactions. It is concluded that the most important transformation of pesticides in the atmosphere is due to reaction with OH radicals. Very few experimental data for pesticides are available though. The levels of uncertainty in OH radical concentrations are acceptable, however, for a proper estimation of atmospheric removal rates due to reactions with OH radicals of those pesticides for which experimental transformation rates (of homologues) are available.     

Atmospheric Dispersion of Current-Use Pesticides: A Review of the Evidence from Monitoring Studies

Recently, evidence has accumulated that the extensive use of modern pesticides results in their presence in the atmosphere at many places throughout the world. In Europe over 80 current-use pesticides have been detected in rain and 30 in air. Similar observations have been made in North America. The compounds most often looked for and detected are the organochlorine insecticide lindane and triazine herbicides, especially atrazine. However, acetanilide and phenoxyacid herbicides, as well as organophosphorus insecticides have also frequently been found in rain and air. Concentrations in air normally range from a few pg/m³ to many ng/m³. Concentrations in rain generally range from a few ng/L to several µg/L. In fog even higher concentrations are observed. Deposition varies between a few mg/ha/y and more than 1 g/ha/y per compound. However, these estimates are usually based on the collection and analysis of (bulk) precipitation and do not include dry particle deposition and gas exchange. Nevertheless, model calculations, analysis of plant tissue, and first attempts to measure dry deposition in a more representative way, all indicate that total atmospheric deposition probably does not normally exceed a few g/ha/y. So far, little attention has been paid to the presence of transformation products of modern pesticides in the atmosphere, with the exception of those of triazine herbicides, which have been looked for and found frequently. Generally, current-use pesticides are only detected at elevated concentrations in air and rain during the application season. The less volatile and more persistent ones, such as lindane, but to some extent also triazines, are present in the atmosphere in low concentrations throughout the year. In agricultural areas, the presence of modern pesticides in the atmosphere can be explained by the crops grown and pesticides used on them. They are also found in the air and rain in areas where they are not used, sometimes even in remote places, just like their organochlorine predecessors. Concentrations and levels are generally much lower there. These data suggest that current-use pesticides can be transported through the atmosphere over distances of tens to hundreds, and sometimes even more than a thousand kilometres. The relative importance of these atmospheric inputs varies greatly. For mountainous areas and remote lakes and seas, the atmosphere may constitute the sole route of contamination by pesticides. In coastal waters, on the other hand, riverine inputs may prevail. To date, little is known about the ecological significance of these aerial inputs.     

Rare Earth Elements and Other Metals in Atmospheric Particulate Matter in the Western Part of The Netherlands

Atmospheric particulate matter (APM) wascollected in Delft, in the western part of theNetherlands, on micro-quartz glass fibre filters fromJuly to September, 1997. The concentrations of rareearth elements (REE) and 9 other metals (Cd, Pb, Fe,V, Ti, Mg, Ca, Na and Al) in the APM were determinedby Inductively Coupled Plasma Mass Spectrometry(ICP-MS) and Inductively Coupled Plasma-AtomicEmission Spectrometry (ICP-AES). The total REE(ΣREE) concentration, light-REE (LREE, includingSc, La, Ce, Pr, Nd, Sm and Eu) concentration, andheavy-REE (HREE, including Gd, Tb, Dy, Ho, Er, Tm, Yb,Lu and Y) concentrations were 0.22–33.0; 0.21–30.68;and 0.01–2.32 ng m^-3, respectively. The ratio ofLREE to HREE ranged from 6.37 to 33.58; the ratio ofLREE to ΣREE was 0.86–0.97, the average being 0.90; and the ratio of HREE to ΣREE was0.03–0.14, with an average of 0.1. The variation ofthe ratio of LREE to ΣREE and HREE to ΣREEwas small. The La to Ce, and La to Sm ratios variedconsiderably i.e. 0.5–4.38 and 4.33–71.42respectively. The variation in concentrations of REEand other metals observed was dependent upon the winddirection and consequently on prevailingmeteorological conditions and anthropogenic activity.     

Environmental Risk Assessment for Pesticides in the Atmosphere; The Results of an International Workshop

The Health Council of the Netherlands organised an international workshop on the fate of pesticides in the atmosphere and possible approaches for their regulatory environmental risk assessment. Approximately forty experts discussed what is currently known about the atmospheric fate of pesticides and major gaps in our understanding were identified. They favoured a tiered approach for assessing the environmental risks of atmospheric dispersion of these chemicals. In the first tier a pesticide's potential for emission during application, as well as its volatilisation potential should be assessed. Estimates of the former should be based on the application method and the formulation, estimates of the latter on a compound's solubility in water, saturated vapour pressure and octanol/water partition coefficient. Where a pesticide's potential for becoming airborne exceeds critical values, it should be subjected to a more rigorous second tier evaluation which considers its toxicity to organisms in non-target areas. This evaluation can be achieved by calculating and comparing a predicted environmental concentration (PEC) and a predicted no-effect concentration (PNEC). By applying an extra uncertainty factor the PNEC can be provisionally derived from standard toxicity data that is already required for the registration of pesticides. Depending on the distance between the source and the reception area, the PEC can be estimated for remote areas using simple dispersion, trajectory type models and for nearby areas using common dispersion models and standard scenarios of pesticide use. A pesticide's atmospheric transport potential is based on factors such as its reaction rate with OH radicals. It should be used to discriminate between those compounds for which only the risks to nearby ecosystems have to be assessed, and those for which the risks to remote ecosystems also have to be determined. The participants were of the opinion that this approach is, in principle, scientifically feasible, although the remaining uncertainties are substantial. Further field and laboratory research is necessary to gain more reliable estimates of the physico-chemical properties of pesticides, to validate and improve environmental fate models and to validate the applicability of standard toxicity data. This will increase both the accuracy of and our confidence in the outcome of the risk assessment.