Soil thresholds and a decision tool to manage food safety of crops grown in chlordecone polluted soil in the French West Indies

Microwave-enhanced thermal removal of organochlorine pesticide (chlordecone) from contaminated soils

Soil contamination with chlordecone, an organochlorine pesticide, is causing serious health problems, affecting crop production and local livestock valorization in the French West Indies. In-situ chemical reduction (ISCR) processes for soil remediation have shown promise but need improvement in terms of time, cost and effective treatment, particularly for andosol soil types. Our study shows that a 10-min microwave treatment significantly reduces chlordecone concentrations (50-90%) in contaminated andosol and nitisol soils. Dry andosol soils show the highest removal yields and reach a higher final temperature (350 °C). Microwave treatment is in all cases more effective or at least as effective as 60 min of conventional heating at a target temperature of 200 °C. The thermal response of andosol and nitisol to microwave exposure is different, as the former is likely to undergo thermal runaway, reaching high temperatures in a short time, resulting in highly efficient thermal removal of chlordecone. These results encourage further scale-up, particularly for the treatment of andosol soils due to their strong microwave response.

A national-scale distribution of organochlorine pesticides (OCPs) in cropland soils and major types of food crops in China: Co-occurrence and associated risks

Organochlorine pesticides (OCPs) are persistent organic pollutants (POPs) that resist degradation in the environment. OCPs remain detectable in cropland systems in China. However, spatial distribution of OCPs across China and associated ecological and health risks, as well as the relationship between levels of OCPs in cropland soils and crops, remain to be elucidated. To fill these gaps, we conducted a national-scale characterization of 19 individual OCPs in cropland soils and food crops including cereals and legumes in China, which were on-spot sampled simultaneously. Sparse canonical correlation analysis was employed to investigate the co-occurrence of OCPs in cropland soils and corresponding food crops. The ecological soil screening levels and risk quotient method were adopted for ecological and health risk assessment, respectively. Dichlorodiphenyltrichloroethanes (DDTs) were dominant in cropland systems, with its levels ranging up to 337 and 22.8 μg/kg in cropland soils and food crops, respectively. The mean ∑OCP levels in cropland soils varied from below the limit of detection to 337 μg/kg. Peanuts were the most contaminated crop, in which endosulfans and hexachlorobenzene (HCB) were co-occurrent with those in cropland soils (correlation coefficient R = 0.999 and 0.947, respectively). Besides, lindane and β-endosulfan in rice were co-occurrent with those in cropland soils (R = 0.810 and 0.868, respectively). The componential ratio analysis indicated fresh inputs of technical DDT, lindane, chlordane, endosulfan, HCB and aldrin. Among these pesticides, ecological impacts of DDTs, lindane, aldrin and β-endosulfan could be expected. Human health risk assessment suggested that daily consumption of the OCP-contaminated food crops raises a health concern especially for male teens. It is concluded that OCPs remain present in cropland systems in China at levels that raise a concern for both environment and human health.

Physical limitation of pesticides (chlordecone) decontamination in volcanic soils: fractal approach and numerical simulation

In the French West Indies, the chlordecone (organochloride pesticide) pollution is now diffuse becoming new contamination source for crops and environment (water, trophic chain). Decontamination by bioremediation and chemical degradation are still under development but the physical limitations of these approaches are generally not taken into account. These physical limitations are related to the poor physical accessibility to the pesticides in soils because of the peculiar structural properties of the contaminated clays (pore volume, transport properties, permeability, and diffusion). Some volcanic soils (andosols), which represent the half of the contaminated soils in Martinique, contain nanoclay (allophane) with a unique structure and porous properties. Andosols are characterized by pore size distribution in the mesoporous range, a high specific surface area, a large pore volume, and a fractal structure. Our hypothesis is that the clay microstructure characteristics are crucial physico-chemical factors strongly limiting the remediation of the pesticide. Our results show that allophane microstructure (small pore size, hierarchical microstructure, and tortuosity) favors accumulation of chlordecone, in andosols. Moreover, the clay microporosity limits the accessibility of microorganisms and chemical species able to decontaminate because of poor transport properties (permeability and diffusion). We model the transport properties by two approaches: (1) we use a numerical model to simulate the structure of allophane aggregates. The algorithm is based on a cluster-cluster aggregation model. From the simulated data, we derived the pore volume, specific surface area, tortuosity, permeability, and diffusion. We show that transport properties strongly decrease because of the presence of allophane. (2) The fractal approach. We characterize the fractal features (size of the fractal aggregate, fractal dimension, tortuosity inside allophane aggregates) and we calculate that transport properties decrease of several order ranges inside the clay aggregates. These poor transport properties are important parameters to explain the poor accessibility to pollutants in volcanic soils and should be taken into account by future decontamination process. We conclude that for andosols, this inaccessibility could render inefficient some of the methods proposed in the literature.

Development and characterisation of a nanostructured hybrid material with vitamin B12 and bagasse-derived activated carbon for anaerobic chlordecone (Kepone) removal

Intensive use of the chlorinated pesticide chlordecone from the 1970s to 1993 to prevent crop damage in banana plantations of Guadeloupe and Martinique led to diffuse pollution of soils and surface waters, affecting both fauna and human beings in the contaminated areas. Since 2001, drinking water production plants have been equipped with filters containing activated carbon that must be treated after saturation. The objective of this work is to produce a hybrid material composed of activated carbon and vitamin B12 (VB12) for the degradation of chlordecone (CLD). The preparation of such a hybrid material is carried out by non-covalent fixation to achieve an eco-friendly solution for the serious environmental problem of contamination by chlorinated pesticides. It is thus proposed to degrade CLD by a physico-chemical treatment allowing salvage of the catalyst, which is adsorbed on the carbon surface to generate less waste that is inexpedient to treat. Activated carbon (AC) is produced locally from available sugarcane bagasse subjected to phosphoric acid activation. The main characteristics of this material are a major mesoporous structure (0.91%) and a specific (BET) surface area ranging from 1000 to 1500 m² g^-1. The experimental results showed that BagP1.5 has a high adsorption capacity for VB12 due to its large surface area (1403 m² g^-1). The binding of VB12 to the bagasse-derived AC is favoured at high temperatures. The adsorption is optimal at a pH of approximately 6. The maximum adsorption capacity of VB12 on the AC, deduced from the Langmuir model, was 306 mg g^-1, confirming the high affinity between the two components. The hybrid material was characterised by FTIR, Raman, X-ray fluorescence spectroscopy and SEM analysis. CLD removal by this hybrid material was faster than that by VB12 or BagP1.5 alone. The CLD degradation products were characterised by mass spectrometry.

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.

Growing food in polluted soils: A review of risks and opportunities associated with combined phytoremediation and food production (CPFP)

Innumerable private households and small-scale producers currently operate on polluted soils. Phytoremediation is one of the most cost-effective remediation options but as a stand-alone technology, it is often not lucrative enough to make it appealing for farmers, especially in economically vulnerable regions. Economic incentives are crucial for remediation projects to materialise and synergies can be obtained by integrating phytoremediation with other profitable activities including food production. This review aims to synthesise state-of-the-art scientific data to provide a general understanding of opportunities and risks for sustainable remediation of agricultural soil by the use of combined phytoremediation and food production (CPFP). The results show that strategies based on CPFP may be appropriate options for most pollutants in virtually all climatic or socioeconomic contexts but a number of challenges need to be surpassed. The challenges include remediation-technological issues such as undeveloped post-harvest technology and inadequate soil governance. The need for remediation solutions for polluted fields is increasingly urgent since many farmers currently operate on polluted land and the scarcity of soil resources as the human population continuously increases will inevitably force more farmers to cultivate in contaminated areas. We conclude that, although large scale CPFP has not yet reached technological maturity, appropriate combinations of soil types, plant species/cultivars, and agronomic practices together with thorough monitoring of the pollutants' pathways can potentially allow for safe food production on polluted soil that restricts the transfer of a number of pollutants to the food chain while the soil pool of pollutants is gradually reduced.

Evidence for extensive anaerobic dechlorination and transformation of the pesticide chlordecone (C10Cl10O) by indigenous microbes in microcosms from Guadeloupe soil

The historic use of chlordecone (C₁₀Cl₁₀O) as a pesticide to control banana weevil infestations has resulted in pollution of large land areas in the French West Indies. Although currently banned, chlordecone persists because it adsorbs strongly to soil and its complex bis-homocubane structure is stable, particularly under aerobic conditions. Abiotic chemical transformation catalyzed by reduced vitamin B₁₂ has been shown to break down chlordecone by opening the cage structure to produce C9 polychloroindenes. More recently these C9 polychloroindenes were also observed as products of anaerobic microbiological transformation. To investigate the anaerobic biotransformation of chlordecone by microbes native to the French West Indies, microcosms were constructed anaerobically from chlordecone impacted Guadeloupe soil and sludge to mimic natural attenuation and eletron donor-stimulated reductive dechlorination. Original microcosms and transfers were incubated over a period of 8 years, during which they were repeatedly amended with chlordecone and electron donor (ethanol and acetone). Using LC-MS, chlordecone and degradation products were detected in all the biologically active microcosms. Observed products included monohydro-, dihydro- and trihydrochlordecone derivatives (C₁₀Cl_10-nO₂H_n; n = 1,2,3), as well as “open cage” C9 polychloroindene compounds (C₉Cl_5-nH_3+n n = 0,1,2) and C10 carboxylated polychloroindene derivatives (C₁₀Cl_4-nO₂H_4+n, n = 0–3). Products with as many as 9 chlorine atoms removed were detected. These products were not observed in sterile (poisoned) microcosms. Chlordecone concentrations decreased in active microcosms as concentrations of products increased, indicating that anaerobic dechlorination processes have occurred. The data enabled a crude estimation of partitioning coefficients between soil and water, showing that carboxylated intermediates sorb poorly and as a consequence may be flushed away, while polychlorinated indenes sorb strongly to soil. Microbial community analysis in microcosms revealed enrichment of anaerobic fermenting and acetogenic microbes possibly involved in anaerobic chlordecone biotransformation. It thus should be possible to stimuilate anaerobic dechlorination through donor amendment to contaminated soils, particularly as some metabolites (in particular pentachloroindene) were already detected in field samples as a result of intrinsic processes. Extensive dechlorination in the microcosms, with evidence for up to 9 Cl atoms removed from the parent molecule is game-changing, giving hope to the possibility of using bioremediation to reduce the impact of CLD contamination.

Transport of chlordecone and two of its derivatives through a saturated nitisol column (Martinique, France)

Soils, surface and groundwater in Martinique (French West Indies) are contaminated by chlordecone (CLD), a highly persistent organochlorine pesticide. In Situ Chemical Reduction (ISCR) using zero valent iron has been tested as a remediation technique to lower CLD levels in soils but it produces derivatives whose fate in environment may differ from the parent molecule. Here, the transfer of CLD and two of its main derivatives resulting from ISCR, CLD5aH and a CLD-3Cl, have been investigated in untreated and treated nitisol from a banana plantation using column experiments (20 cm long and 2.5 cm in diameter) under saturated conditions. The circulation of CaCl₂ 10^-2M solution, simulating the ionic strength of soil water, in untreated nitisol results in CLD concentrations in solutions that remain for decades above the threshold limit for drinking water. ISCR treatment lowers the CLD concentration by ~50% in soil and by a factor 3 in waters but they remain above the threshold values. CLD derivatives, CLD5aH and a CLD-3Cl and, to a lesser extent, a CLD-2Cl and a CLD-5Cl, are found in waters after treatment. Dechlorination increases the mobility of the derivatives with respect to the parent molecule, which is likely to induce their transfer to deeper soil layers than those treated by ISCR: CLD-3Cl is more mobile than CLD5aH which is more mobile than CLD. When the water is in contact with the contaminated soil, a period of fast desorption kinetic of CLD and its derivatives, followed by a period of slow kinetics are found. This attests the high risk for water contamination and the potential influence of rainfall events on the concentrations likely to be encountered in soil waters or in waters accumulated on the soil surface.

Natural Chlordecone Degradation Revealed by Numerous Transformation Products Characterized in Key French West Indies Environmental Compartments

Production and use of the insecticide chlordecone has caused long-term environmental pollution in the James River area and the French West Indies (FWI) that has resulted in acute human-health problems and a social crisis. High levels of chlordecone in FWI soils, even after its ban decades ago, and the absence of detection of transformation products (TPs), have suggested that chlordecone is virtually nonbiodegradable in the environment. Here, we investigated laboratory biodegradation, consisting of bacterial liquid cultures and microcosms inoculated with FWI soils, using a dual nontargeted GC-MS and LC-HRMS approach. In addition to previously reported, partly characterized hydrochlordecones and polychloroindenes (families A and B), we discovered 14 new chlordecone TPs, assigned to four families (B, C, D, and E). Organic synthesis and NMR analyses allowed us to achieve the complete structural elucidation of 19 TPs. Members of TP families A, B, C, and E were detected in soil, sediment, and water samples from Martinique and include 17 TPs not initially found in commercial chlordecone formulations. 2,4,5,6,7-Pentachloroindene was the most prominent TP, with levels similar to those of chlordecone. Overall, our results clearly show that chlordecone pollution extends beyond the parent chlordecone molecule and includes a considerable number of previously undetected TPs. Structural diversity of the identified TPs illustrates the complexity of chlordecone degradation in the environment and raises the possibility of extensive worldwide pollution of soil and aquatic ecosystems by chlordecone TPs.