Transfer Pathways and Fluxes of Water-Soluble Pesticides in Various Compartments of the Agricultural Catchment of the Canche River (Northern France)

Abstract

Five frequently used water-soluble pesticides (atrazine, diflufenican, metolachlor, pendimethalin, and ethofumesate) were monitored in surface water and groundwater of an agricultural catchment (Canche River) in Northern France for examining the edge-of-field pathways of substances and their characteristic time of transport. The study of surface water contamination was conducted in 2016 through two time scales: continuously over one year at a single location of the catchment and punctually during four seasons at 15 sampling locations along a longitudinal river profile. In addition, groundwater in winter and summer shows a generally low and relatively constant contamination level. Nevertheless, the outflow of pesticides from groundwater results in a background contamination of surface water. In addition to this, a contamination peak above the baseline level is observed in surface water subsequently to the period of substance application on the fields. Our results show that pesticides were essentially transported into the surface water by fast flow components (runoff water). Loss of pesticides during the contamination peak period and long-term monitoring were compared showing that the transport of substances within weeks after pesticides spreading dominates the annual flux of pesticides, except for atrazine which shows a constant background contamination pattern. Low frequency monitoring schemes provide only a partial picture of the contamination state and do not enable to evaluate the true contamination state of such rivers with regard to the fact that 3/4 of the annual load of pesticides are transported in the stream during only 2–3 months.

Multiyear and seasonal global indicators for French surface waters contamination by WFD substances

“…Many studies have reported PPP active substances contamination peaks in streams at the local scale, subsequent to rain events occurring upon the treated fields (Castle 2018, Belles 2019. These "flushes" may occur through very limited time periods (e.g.…”

Impacts of chemical stress, season, and climate change on the flounder population of the highly anthropised Seine estuary (France)

“…Despite a significant improvement of the Seine water quality during the last two decades, the Seine is still considered one of the most chemically polluted estuaries in western northern Europe (Poisson et al 2011;Burgeot et al 2017). The Canche estuary (average annual flow 21 m 3 /s) is a small system (water catchment 1,300 km 3 ) displaying a reduced anthropisation characterized by a low urban development without strong industrialisation; thus, this estuary is considered to be moderately polluted (Henry et al 2012;Belles et al 2019).…”

“…Despite a significant improvement of the Seine water quality during the last decades (Fisson et al 2014), the Seine estuary still shows very high levels of PCBs in flounder linked to intensive industrial activities, and to the high concentrations of persistent organic pollutants in the sediments (Tappin and Millward 2015). On the other hand, the Canche system is an agricultural catchment displaying reduced levels of pesticides, and limited sources of organic pollutants (Belles et al 2019). Concerning the heavy metal pollution, the highest flux of metals over the Eastern Channel is related to the heritage of a strong historical pollution over the Seine basin (Fisson et al 2017), and to the dumping of dredged spoil and domestic wastes or the discharge from the industry sector in the Seine estuary (Tappin and Millward 2015).…”

Continuous high-frequency pesticide monitoring in a small tile-drained agricultural stream to reveal diel concentration fluctuations in dry periods

“…Plant protection products (PPPs) use promises to achieve global food security (Popp et al, 2012), but the consequent environmental contamination poses a global environmental hazard (Stehle and Schulz, 2015;Maggi et al, 2020). It is the common view that surface waters are predominantly exposed to high concentrations of PPPs during rain events (Schulz, 2001;Szocs et al, 2017) and to transformation products (TPs) in dry periods (Rasmussen et al, 2015;Spycher et al, 2018;Belles et al, 2019;Sanford and Prosser, 2020;Halbach et al, 2021;Le Cor et al, 2021). Given the large effort that goes with sampling and analyzing PPPs from streams, many studies increase sampling frequency in response to hydrological proxies, such as rainfalls or increments in discharge in accordance with the scientific evidence showing that the largest loads of PPPs in water bodies occur during rain events (Doppler et al, 2012;Halbach et al, 2021).…”

“…It is known that irrigation can drive substantial leaching of herbicides from maize fields (Giuliano et al, 2021) and numerical modeling also supports the relevance of this practice to leaching (la Cecilia et al, 2020). Groundwater can be the carrier of PPPs and TPs stored in the catchment (Belles et al, 2019;Welch et al, 2019;Le Cor et al, 2021). Groundwater can also deliver legacy contaminants (Rasmussen et al, 2015), some of which may still be under mandatory monitoring in Europe due to their health and environmental risk as prescribed by the Water Framework Directive (EC, 2013) (e.g., the herbicide atrazine).…”