This special issue of Environmental Science and Pollution Research gathers selected papers presented at the 48th and 49th congresses of the French pesticide research group (Groupe Français de recherches sur les Pesticides, GFP) that took place in May 2018 and May 2019 in Limoges and Montpellier, France, respectively. The congresses of GFP review the knowledge acquired by the French-speaking scientific community in all areas relating to pesticides. This includes their effectiveness, modes of action and fate in the different compartments of ecosystems, the remediation processes, the metrology and monitoring approaches, the methods of diagnosis and modelling of contamination and impacts. The GFP congresses are an opportunity to cross-fertilise expertise in various disciplinary fields: analytical developments, toxicological and ecotoxicological impacts of pesticides, fate of compounds into the environment, curative and alternative solutions.

The 48th edition focused on “Pesticide metrology and risk assessment for humans and the natural environment” with highlights on headwaters contamination with pesticides and their by-products the third day of the congress. Other aspects of research about pesticides were also presented and discussed including metrology and analytical methods for monitoring pesticides, pesticides and human health: exposure of users and consumers, pesticides and networks (rainwater, drinking water and wastewater), alternative methods and agro-ecology, impacts on ecosystems: chronic/acute toxicity, passive/active exposure, pesticides, environmental law and environmental policy (national, European) and societal perceptions of pesticide-related issues. About forty oral presentations and eight poster presentations were given during three days with more than 120 participants. During the 48th Congress, special attention was paid to the transfer of scientific advances to actors on the ground, but also to the general public. Thus, a full day of the congress was dedicated to various conferences presenting different aspects on the trend of pesticides in an urban environment or in the headwaters context with passionate debates around the interest of regulating the research about particular herbicides by-products. The 48th GFP congress ended with a series of conferences given by members of the laboratory of the University of Limoges and the NGO OIEau (www.oieau.fr) to provide objective and factual information to the general public. The debate in France in 2018 about the effect of glyphosate and neonicotinoids on humans or on bees, respectively, was important between all stakeholders. This series of conferences was an opportunity to discuss with actors on the field and the general public with scientific bases. This allowed each participant to make its own opinion on the interest of the use of phytosanitary products allowing a clear progress in agriculture in order to ensure food production for a growing world population and an increasingly highlighted health and environmental impact.

The 49th congress in Montpellier focused on the theme “Pesticides and agro-ecological transition: challenges and progress”, with particular attention to the countries of the Mediterranean basin. Indeed, the use of pesticides in agriculture and their impact on the environment and human health is a subject that has been regularly addressed for many years in the public and political debate in France. In 2008, a phase of consultation (Grenelle de l’Environnement) of state and local authorities, trade unions, NGOs and public led to the objective of reducing the use of these products by 50% in France. After more than a decade, it is clear that this objective has not been achieved despite the efforts made. In link with this aim of reducing pesticide use, research activities have evolved as could be seen in the 82 oral and poster presentations at the 49th GFP congress. The papers presented indicate a strengthening of the work on improving our understanding and reducing the use of pesticides, and on the impacts of spraying on both biological organisms and landscapes. In particular, it highlighted a significant potential for reducing the quantities of pesticides applied without reducing the effectiveness of plant protection by using more efficient application tools that limit the drift phenomenon as much as possible. The decisive influence of sociological factors and training on the use of pesticides was illustrated in several papers. In terms of diagnosing environmental contamination by pesticides, the congress showed that all matrices—soil, water, air, plants and animals—are now being studied. This is a step towards a more systemic and comprehensive study of the impacts of pesticide use. The presentation of new pesticide analysis techniques based on high-resolution mass spectrometry detection favours this evolution since these techniques allow the search for a greater number of molecules in the samples studied. The work presented on the impacts on human health was diversified, ranging from studies on the exposure of the general population to that of applicators and people living near spraying operations, but also to the study of the physiological mechanisms induced by exposure. Finally, we underline the emergence of numerous works for the observation and modelling of the influence of the organisation and management of cultivated landscapes on the dispersion of pesticides and their ecotoxicological impacts. This marked extension of the spatial scale of study of the fate of pesticides in the environment answers the objective of better understanding the pollution pressures exerted on biological populations, but also answers the aim of searching levers for the agroecological management of cultivated ecosystems that enhance biodiversity.

Amongst all presentations made at the two congresses, this special issue gathers 5 papers. They represent only a small part of the subjects discussed at the two congresses, but illustrate the major concerns about the understanding and monitoring of the contamination by pesticides of ecosystem compartments.

A main challenge in the management of water pollution at the catchment level is to identify vulnerability zones where priority actions should be taken to limit the pollution risks. The methodologies for mapping these zones are constantly improving thanks to the development of higher-resolution data bases including a wider range of geographic, agricultural and hydrological data and to improved spatial analysis and mapping procedures. Grimene et al. (2021) present a recently developed mapping methodology of vulnerability zones to pesticide pollution that considers 11 vulnerability factors of agricultural or pedoclimatic origin. They illustrate their methodology on the case of the 820 km2 Gimone watershed where 70% of land use is intensive cropland.

Another important issue in water pollution management is the ability to monitor water quality over networks of sampling spots. Current monitoring procedure of surface waters still rely on low frequency grab sampling, which does not ensure unbiased estimation of either average or peak pollution levels. Passive samplers have been developed to offer an integrative measurement capacity of several weeks. However, as stressed by Bernard et al. (2018), there is little experience about whether passive sampler can also catch peak contamination events. Bernard et al. (2018) therefore evaluated in a lab experiment the capacity of the Polar Organic Chemical Integrative Samplers (POCIS) to record such events for a range of pesticides with different polarities.

The environmental fate of chlordecone, a very persistent organochlorine massively applied in the banana fields of the French West Indies between 1972 and 1993, is still a major concern for French environmental researchers as it contaminated severely the terrestrial and marine ecosystems of these Caribbean islands,. Two papers in this special issue investigate some of the processes that lead to the contamination of coastal ecosystems by means of chlordecone runoff from the contaminated watersheds. In one paper, Dromard et al. (2019) examined the consistency of three hypothesis: (i) chlordecone can stay sorbed on the volcanic soils particles during their transfer from contaminated soils to the marine environment, (ii) zooplankton can represent a major pathway of chlordecone to the trophic marine food chain, (iii) chlordecone concentrates in marine organisms, depending on their proximity to the source of chlordecone and their feeding ecology. To this aim, Dromard et al. (2019) combined a desorption study of chlordecone in saline water from allophanes, a major amorphous mineral of the volcanic soils, and the measurement of contamination of the trophic food chain in mangroves, seagrass beds and coral reefs. In the other paper, Devault et al. (2021) investigated the processes of contamination and decontamination by chlordecone and arsenic of Sargassum sp. that accumulates regularly on the Caribbean beaches since 2011 and causes severe nuisance. Indeed, possible contamination of these algae on the beaches has to be considered in their treatment plans. Therefore, Devault et al. (2021) performed in situ and mesocosm experiments to analyse the specific kinetics of adsorption and desorption of both compounds to Sargassum sp. in coastal conditions.

A last concern highlighted in this special issue is the contamination of untreated fields and areas by pesticides. Devault et al. (2019) examine the possible ways of dispersion of prosulfocarb, a dithiocarbamate that is increasingly used as a pre-emergence herbicide given the ban of some herbicides and developing bioresistance of weeds to others. They review published and official data on Prosulfocarb physico-chemical properties and on its detection in various media to discuss the risks of Prosulfocarb in contaminating untargeted environmental compartments.