Effects of season and sediment-water exchange processes on the partitioning of pesticides in the catchment environment: implications for pesticides monitoring.

Current and historic pesticide use has potential to compromise e.g. drinking water sources due to both primary and secondary emission sources. Understanding the spatial and temporal dynamics of emissions might help inform management decisions. To explore this potential; water, sediment and soil samples were concurrently collected from the River Ugie, Scotland over four seasons. Occurrence and fate of nine pesticides including four historic-use pesticides (HUPs): simazine, atrazine, isoproturon and permethrin, and five current-use pesticides (CUPs): metaldehyde, chlorpyrifos, chlortoluron, epoxiconazole and cypermethrin were analysed. Concentrations of target pesticides in water, sediments and soils were 4.5–45.6 ng·L−1, 0.9–4.6 ng·g−1 dw (dry weight) and 1.7–8.0 ng·g−1 dw, respectively. Concentrations of pesticides in water were found to significantly differ between seasons (p [less than] 0.05). Significant differences in pesticide concentrations also occurred spatially within sediments (p[less than]0.01), indicating spatial and temporal associations with pesticide use. Sediment-water exchange showed that the sediment acts as an important secondary emission source particularly for the HUPs, while current local application and sediment emission are both major driving forces for CUPs in the riverine environment. These findings were supported by concentration ratios between different media, which showed potential as a preliminary assessment tool for identifying the source of pollutants in aquatic environments

Long-term spatial and temporal patterns of polycyclic aromatic hydrocarbons (PAHs) in Scottish soils over 20 years (1990–2009): a national picture.

Long-term spatial and temporal concentrations of polycyclic aromatic hydrocarbons (PAHs) in Scottish soils from four transects were measured in three national-scale surveys conducted between 1990 and 2009. Measured concentrations of 16 priority PAHs ranged from 15,690 to 83.7 ng g−1, with an average of 3659 ± 3131 to 727 ± 654 ng g−1, of which the high molecular weight (HMW) PAHs (4–6 rings) accounted for 73.9 to 89.6%. Overall, concentrations of PAHs in the soil have decreased over time, but the proportion of carcinogenic ∑PAH7 has increased. Concentrations of total PAHs correlated significantly with latitude (R = −0.345, p = 0.001). A significant correlation was found between concentrations of PAHs and soil organic carbon (SOC, R = 0.439, p = 0.000), which is an important factor, influencing the levels of PAHs in soils. Source apportionment analysis indicated that the emission sources of PAHs have evolved from coal and biomass combustion to more diverse sources during the two decades covered by the surveys. It is likely that this reflects societal development towards a lower carbon economy and less use of biomass buring for domestic space heating

Evaluation of spot and passive sampling for monitoring, flux estimation and risk assessment of pesticides within the constraints of a typical regulatory monitoring scheme.

In many agricultural catchments of Europe and North America, pesticides occur at generally low concentrations with significant temporal variation. This poses several challenges for both monitoring and understanding ecological risks/impacts of these chemicals. This study aimed to compare the performance of passive and spot sampling strategies given the constraints of typical regulatory monitoring. Nine pesticides were investigated in a river currently undergoing regulatory monitoring (River Ugie, Scotland). Within this regulatory framework, spot and passive sampling were undertaken to understand spatiotemporal occurrence, mass loads and ecological risks. All the target pesticides were detected in water by both sampling strategies. Chlorotoluron was observed to be the dominant pesticide by both spot (maximum: 111.8 ng/l, mean: 9.35 ng/l) and passive sampling (maximum: 39.24 ng/l, mean: 4.76 ng/l). The annual pesticide loads were estimated to be 2735 g and 1837 g based on the spot and passive sampling data, respectively. The spatiotemporal trend suggested that agricultural activities were the primary source of the compounds with variability in loads explained in large by timing of pesticide applications and rainfall. The risk assessment showed chlorotoluron and chlorpyrifos posed the highest ecological risks with 23% of the chlorotoluron spot samples and 36% of the chlorpyrifos passive samples resulting in a Risk Quotient greater than 0.1. This suggests that mitigation measures might need to be taken to reduce the input of pesticides into the river. The overall comparison of the two sampling strategies supported the hypothesis that passive sampling tends to integrate the contaminants over a period of exposure and allows quantification of contamination at low concentration. The results suggested that within a regulatory monitoring context passive sampling was more suitable for flux estimation and risk assessment of trace contaminants which cannot be diagnosed by spot sampling and for determining if long-term average concentrations comply with specified standards