Compost addition reduces porosity and chlordecone transfer in soil microstructure

Chlordecone (kepone or CLD) was formerly used in French West Indies as an insecticide. Despite its formal ban in 1993, high levels of this pesticide are still found in soils. As such, sequestering matrices like biochars or activated carbons (ACs) may successfully decrease the bioavailability of halogenated compounds like CLD when added to contaminated soils. The present study intends (i) to produce contrasted sequestering matrices in order to (ii) assess their respective efficiency to reduce CLD environmental availability. Hence, the work was designed following two experimental steps. The first one consisted at producing different sequestering media (biochars and ACs) via pyrolysis and distinct activation processes, using two lignocellulosic precursors (raw biomass): oak wood (Quercus ilex) and coconut shell (Cocos nucifera). The chemical activation was carried out with phosphoric acid while physical activation was done with carbon dioxide and steam. In the second step, the CLD environmental availability was assessed either in an OECD artificial soil or in an Antillean contaminated nitisol (i.e. 2.1 µg CLD per g of soil Dry Matter, DM), both amended with 5wt% of biochar or 5wt% of AC.

Section: Comparison Of Strategies Applied To Limit Cld Transfer To Fl...mentioning

confidence: 99%

Reduction of chlordecone environmental availability by soil amendment of biochars and activated carbons from lignocellulosic biomass

Ranguin¹,

Jean-Marius²,

Yacou³

et al. 2020

“…As a result, the only agricultural practices that could have increased CLD leaching are the one that modified environmental characteristics that affect pesticide transfers (Mottes et al 2014). Here, modifications of the soil organic matter content, allophane clay content, or both potentially decreased CLD retention by soil (Woignier et al 2016;Woignier et al 2012a;Woignier et al 2012b;Woignier et al 2013). It has been shown that the peculiar hierarchical (fractal) microstructure of allophane clay traps CLD (Woignier et al 2012a;Woignier et al 2013).…”

Section: Effects Of Cropping Practicesmentioning

confidence: 99%

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

Mottes

Deffontaines

Charlier

et al. 2019

Self Cite

Chlordecone, applied on soils until 1993 to control banana weevil, has polluted waters 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 question the interactions between practices and the environment that induce such variability. We analyzed hydrological and water pollution datasets from a two years monitoring program on the Galion watershed in Martinique (French West Indies). We conjointly analyzed: i) weekly 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 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 conditionsnotably drying periodsand 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.

“…Soil amendments have been shown to influence soil pesticide processes like leaching and degradation (Cox et al 2001;Thevenot et al 2009). We have recently proposed an alternative to the complete decontamination (Clostre et al 2014b;Woignier et al 2013Woignier et al , 2016: the sequestration by the addition of compost. We showed that the addition of 5 wt% of compost strongly decreases the soil-to-water and to vegetables transfers of CLD (pot experiments).…”

Section: Alternative Techniques To Decontaminationmentioning

confidence: 99%

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

Woignier

Rangon

Clostre³

et al. 2019

Self Cite

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.