Two sampling strategies for an overview of pesticide contamination in an agriculture-extensive headwater stream

Abstract

Two headwaters located in southwest France were monitored for 3 and 2 years (Auvézère and Aixette watershed, respectively) with two sampling strategies: grab and passive sampling with polar organic chemical integrative sampler (POCIS). These watersheds are rural and characterized by agricultural areas with similar breeding practices, except that the Auvézère watershed contains apple production for agricultural diversification and the downstream portion of the Aixette watershed is in a peri-urban area. The agricultural activities of both are extensive, i.e., with limited supply of fertilizer and pesticides. The sampling strategies used here give specific information: grab samples for higher pesticide content and POCIS for contamination background noise and number of compounds found. Agricultural catchments in small headwater streams are characterized by a background noise of pesticide contamination in the range of 20-70 ng/L, but there may also be transient and high-peak pesticide contamination (2000-3000 ng/L) caused by rain events, poor use of pesticides, and/or the small size of the water body. This study demonstrates that between two specific runoff events, contamination was low; hence the importance of passive sampler use. While the peak pesticide concentrations seen here are a toxicity risk for aquatic life, the pesticide background noise of single compounds do not pose obvious acute nor chronic risks; however, this study did not consider the risk from synergistic "cocktail" effects. Proper tools and sampling strategies may link watershed activities (agricultural, non-agricultural) to pesticides detected in the water, and data from both grab and passive samples can contribute to discussions on environmental effects in headwaters, an area of great importance for biodiversity.

Trends in the use of passive sampling for monitoring polar pesticides in water

“…The timing and frequency of sampling, location and number of sampling sites, and the duration of monitoring are all important considerations [11,19,34]. The frequency of sampling and duration of monitoring should consider the dynamic range of pesticide concentration and variability over time to ensure that peak concentrations are not missed, and long-term trends are correctly interpreted [35]. Likewise, the timing of sampling should consider the hydrological system and the influence of events such as rainfall to peak concentrations [36][37][38].…”

“…Field applications including device performance has been extensively investigated in comparative studies assessing various PSDs [8,12,36,89,119], and other sampling methods [8,9,42,43,84,115] for pesticides in a range of aqueous matrices. Other field applications have focused on passive sampling within the context of regulatory monitoring [11,32,120], and to optimise strategies to characterise pesticide flux and identify analytes originating from episodic or continuous sources within passive sampling data [35,116]. A significant portion of the literature for each PSD concerns calibration and performance, including the influence of ambient conditions on uptake [103,108,121].…”

“Modern agriculture” transfers many pesticides to watercourses: a case study of a representative rural catchment of southern Brazil

“…Challis et al (2018), also in Canada (Red River -Lake Winnipeg), showed that using POCIS was possible to estimate the main sources of pesticides (i.e., atrazine from the United States and neonicotinoid both from Canadian and the United States agriculture fields) and signaled the time-scale concerning application and detection in surface water. Guibal et al (2017), working in headwaters in two small catchments in France, aware to difficulty for monitoring the pesticides frequency and concentration fluctuation using active or passive sampling. They identified the three possible types of behavior (active >, = and < POCIS) when compared grab and passive sampling in relation to pesticides concentration.…”

Experimental Estimation of 44 Pharmaceutical Polar Organic Chemical Integrative Sampler Sampling Rates in an Artificial River under Various Flow Conditions

“…Quality assurance and control were used to control all deviations arising during analysis. The details of this analytical procedure were previously given and are described in the Supplemental Data of Guibal et al (2015a, 2018b).…”