Aix Marseille Université, Univ Avignon, CNRS, IRD, IMBE, Marseille, France.
IRD, UMR IMBE, Campus Agro-environnemental Caraïbe, Le Lamentin, Martinique, France.
Environ Sci Pollut Res Int. 2020 Nov;27(33):40980-40991. doi: 10.1007/s11356-019-05899-0. Epub 2019 Jul 29.
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.
在法属西印度群岛，十氯酮（有机氯农药）污染现已扩散，成为作物和环境（水、食物链）的新污染源。通过生物修复和化学降解进行的去污仍在开发中，但这些方法的物理限制通常未被考虑在内。这些物理限制与农药在土壤中难以获得有关，这是由于受污染的粘土的特殊结构特性（孔体积、传输特性、渗透性和扩散性）。马提尼克岛一半的污染土壤为火山土壤（火山灰土），其中含有纳米粘土（埃洛石），具有独特的结构和多孔特性。火山灰土的特点是中孔范围内的孔径分布、大的比表面积、大的孔体积和分形结构。我们的假设是，粘土微观结构特征是限制农药修复的关键物理化学因素。我们的研究结果表明，埃洛石微观结构（小孔尺寸、层次微观结构和曲折度）有利于十氯酮在火山灰土中的积累。此外，由于较差的传输特性（渗透性和扩散性），粘土微孔限制了能够去污的微生物和化学物质的可及性。我们通过两种方法来模拟传输特性：（1）我们使用数值模型来模拟埃洛石聚集体的结构。该算法基于簇-簇聚集模型。从模拟数据中，我们得出了孔体积、比表面积、曲折度、渗透性和扩散性。我们表明，由于埃洛石的存在，传输特性会大大降低。（2）分形方法。我们对分形特征（分形聚集体的大小、分形维数、埃洛石聚集体内的曲折度）进行了表征，并计算出粘土聚集体内部的传输特性降低了几个数量级。这些较差的传输特性是解释火山土中污染物难以进入的重要参数，应该在未来的去污过程中加以考虑。我们得出结论，对于火山灰土来说，这种难以接近性可能会使文献中提出的一些方法效率降低。
