Ecotoxicity of chlorophenolic compounds depending on soil characteristics.

Three chlorophenolic compounds (2-chlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol) were tested to assess their effects on two soils with different properties: a granitic soil (Haplic Arenosol) and a calcareous one (Calcaric Regosol). Different concentrations of the pollutants (ranging from 0.001 to 10,000 mg kg(-1) soil, d.w.) were assayed for their effects on soil microbial activity and composition, using manometric respirometry and PCR-DGGE analysis, respectively. Other ecotoxicity tests such as Lactuca sativa seedling growth in the contaminated soils and algal growth inhibition (Pseudokirschneriella subcapitata) in their water extracts were done. The behaviour of the pollutants in the soils with respect to biodegradability and volatilization was also investigated. In the Haplic Arenosol, volatilization is the main process affecting 2-chlorophenol. Degradation and fixation of this compound in the soil matrix are favored in the Calcaric Regosol. This is the least toxic pollutant assayed. For 2,4,6-trichlorophenol, the soil pH is a critical parameter in the toxicity assays due to the neutral pKa of the compound. It is toxic in the soil microbial activity assay, but some recovery of the biotic processes can be observed, particularly in the Calcaric Regosol. This compound is more toxic in the Haplic Arenosol than in the Calcaric Regosol. Pentachlorophenol is ionized in both soils due to its low pKa, increasing its water solubility. It is highly toxic to the soil microbiota, thus inhibiting respiration, biodegradation and other biotic dissipation processes. Plant and alga tests, were more sensitive than soil microbial tests, except for PCP. The microbial populations tend to show changes at lower concentrations than the microbial activity. Some soil types (abundant in the Mediterranean area), with alkaline pH and fine textures could show higher level of ecotoxicity for ionizable organic pollutants than the soil type recommended by the OECD in ecotoxicity testing.