Flow patterns and pathways of legacy and contemporary pesticides in surface waters in tropical volcanic catchments.

Severe water pollution issues due to legacy and contemporary pesticides exist in tropical regions and are linked to cash crops requiring intensive plant protection practices. This study aims to improve knowledge about contamination routes and patterns in tropical volcanic settings to identify mitigation measures and analyse risk. To this aim, this paper analyses four years of monitoring data from 2016 to 2019 of flow discharge and weekly pesticide concentrations in the rivers of two catchments grown predominantly with banana and sugar cane in the French West Indies. The banned insecticide chlordecone, applied in banana fields from 1972 to 1993, was still the major source of river contamination, while the currently used herbicide glyphosate, its metabolite aminomethylphosphonic acid (AMPA), and postharvest fungicides also exhibited high contamination levels. A value of 0.5 of the Gustafson Ubiquity Score (GUS) was shown to separate contaminant and noncontaminant pesticides, indicating a high vulnerability to pollution by pesticides in this tropical volcanic context. The patterns and routes of river exposure to pesticides differed markedly between the pesticides in accordance with the hydrological behaviour of volcanic islands and the history and nature of pesticide uses. Concerning chlordecone and its metabolites, observations confirmed previous findings of a main subsurface origin of river contamination by this compound but also showed large erratic short-term variations, suggesting the influence of fast surface transport processes such as erosion for legacy pesticides with large sorption capacity. Concerning herbicides and postharvest fungicides, observations have suggested that surface runoff and fast lateral flow in the vadose zone control river contamination. Accordingly, mitigation options need to be considered differently for each type of pesticide. Finally, this study points out the need for developing specific exposure scenarios for tropical agricultural contexts in the European regulation procedures for pesticide risk assessment.

Long-term pollution by chlordecone of tropical volcanic soils in the French West Indies: New insights and improvement of previous predictions.

Chlordecone (CLD), was widely applied in banana fields in the French West Indies from 1972 to 1993. The WISORCH model was constructed to assess soil contamination by CLD and estimated that it lasts from 100 to 600 years, depending on leaching intensity and assuming no degradation. However, recent studies demonstrated that CLD is degraded in the environment, hence questioning the reliability of previous estimations. This paper shows how to improve the model and provides insights into the long-term dissipation of CLD. In-situ observations were made in nearly 2545 plots between 2001 and 2020, and 17 plots were sampled at two dates. Results of soil analyses showed an unexpected 4-fold decrease in CLD concentrations in the soil, in contrast to simulations made using the first version of WISORCH at the time. Neither erosion, nor CLD leaching explained these discrepancies. In a top-down modeling approach, these new observations of CLD concentrations led us to implement a new dissipation process in the WISORCH model that corresponds to a DT50 dissipation half-life of 5 years. The new version of the improved model allowed us to update the prediction of the persistence of soil pollution, with soil decontamination estimated for the 2070s. This development calls for re-evaluation of soil pollution status. Further validation of the new version of WISORCH is needed so it can contribute to crop management on contaminated soil.

Evidence of Chlordecone Resurrection by Glyphosate in French West Indies.

The widespread use of pesticides in agriculture during the last several decades has contaminated soils and different Critical Zone (CZ) compartments, defined as the area extended from the top of the vegetation canopy to the groundwater table, and it integrates interactions of the atmosphere, lithosphere, biosphere, and hydrosphere. However, the long-term fate, storage, and transfer dynamics of persistent pesticides in CZ in a changing world remain poorly understood. In the French West Indies, chlordecone (CLD), a toxic organochlorine insecticide, was extensively applied to banana fields to control banana weevil from 1972 to 1993 after which it was banned. Here, to understand CZ trajectories we apply a retrospective observation based on marine sediment core analyses to monitor long-term CLD transfer, fate, and consequences in Guadeloupe and Martinique islands. Both CLD profiles show synchronous chronologies. We hypothesized that the use of glyphosate, a postemergence herbicide, from the late 1990s onward induced CZ modification with an increase in soil erosion and led to the release of the stable CLD stored in the soils of polluted fields. CLD fluxes drastically increased when glyphosate use began, leading to widespread ecosystem contamination. As glyphosate is used globally, ecotoxicological risk management strategies should consider how its application affects persistent pesticide storage in soils, transfer dynamics, and widespread contamination.

Spatio-temporal variability of water pollution by chlordecone at the watershed scale: what insights for the management of polluted territories?

Chlordecone, applied on soils until 1993 to control banana weevil, has polluted water resources in the French West Indies for more than 40 years. At the watershed scale, chlordecone applications were not homogenous, generating a spatial heterogeneity of the pollution. The roles of climate, hydrology, soil, agronomy, and geology on watershed functioning generate a temporal heterogeneity of the pollution. This study questions the interactions between practices and the environment that induce such variability. We analyzed hydrological and water pollution datasets from a 2-year monitoring program on the Galion watershed in Martinique (French West Indies). We conjointly analyzed (i) weekly chlordecone (CLD) concentration monitored on 3 river sampling sites, (ii) aquifer piezometric dynamics and pollutions, and (iii) agricultural practices on polluted soils. Our results showed that chlordecone pollution in surface waters are characterized by annual trends and infra-annual variations. Aquifers showed CLD concentration 10 times higher than surface water, with CLD concentration peaks during recharge events. We showed strong interactions between rainfall events and practices on CLD pollution requiring a systemic management approach, in particular during post-cyclonic periods. Small sub-watershed with high CLD pollution appeared to be a substantial contributor to CLD mass transfers to the marine environment via rivers and should therefore receive priority management. We suggest increasing stable organic matter return to soil as well as external input of organic matter to reduce CLD transfers to water. We identified hydrological conditions-notably drying periods-and tillage as the most influential factors on CLD leaching. In particular, tillage acts on 3 processes that increases CLD leaching: organic matter degradation, modification of water paths in soil, and allophane clay degradation.

RECOTOX, a French initiative in ecotoxicology-toxicology to monitor, understand and mitigate the ecotoxicological impacts of pollutants in socioagroecosystems.

RECOTOX is a cross-cutting initiative promoting an integrated research to respond to the challenges of monitoring, understanding, and mitigating environmental and health impacts of pesticides in agroecosystems. The added value of RECOTOX is to develop a common culture around spatial ecotoxicology including the whole chain of pressure-exposure-impact, while strengthening an integrated network of in natura specifically equipped sites. In particular, it promotes transversal approaches at relevant socioecological system scales, to capitalize knowledge, expertise, and ongoing research in ecotoxicology and, to a lesser extent, environmental toxicology. Thus, it will open existing research infrastructures in environmental sciences to research programs in ecotoxicology of pesticides.

Watershed-scale assessment of oil palm cultivation impact on water quality and nutrient fluxes: a case study in Sumatra (Indonesia).

High fertilizer input is necessary to sustain high yields in oil palm agroecosystems, but it may endanger neighboring aquatic ecosystems when excess nutrients are transported to waterways. In this study, the hydrochemical dynamics of groundwater and streams under baseflow conditions were evaluated with bi-monthly measurements for 1 year on 16 watersheds. Hydrochemical measurements were related to the spatial distribution of soil and fertilization practices across a landscape of 100 km(2), dominated by oil palm cultivation, in Central Sumatra, Indonesia. The low nutrient concentrations recorded in streams throughout the landscape indicated that the mature oil palm plantations in this study did not contribute to eutrophication of aquatic ecosystems. This was ascribed to high nutrient uptake by oil palm, a rational fertilizer program, and dilution of nutrient concentrations due to heavy rainfall in the study area. Soil type controlled dissolved inorganic N and total P fluxes, with greater losses of N and P from loamy-sand uplands than loamy lowlands. Organic fertilization helped to reduce nutrient fluxes compared to mineral fertilizers. However, when K inputs exceeded the oil palm requirement threshold, high K export occurred during periods when groundwater had a short residence time. For higher nutrient use efficiency in the long term, the field-scale fertilizer management should be complemented with a landscape-scale strategy of fertilizer applications that accounts for soil variability.