Temperature and organic matter dependence of the distribution of organochlorine compounds in mountain soils from the subtropical Atlantic (Teide, Tenerife Island).

Surface soil samples from Teide mountain (Canary Islands) have been analyzed for polychlorobiphenyls (PCBs), DDTs, hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), and pentachlorobenzene. The samples were situated between 10 and 3400 m above sea level being distributed below, at, and above the permanent inversion layer system characteristic of the subtropical Atlantic. All OC concentrations were, in general, low when compared with the data from urban, agricultural, or woodland soils reported elsewhere. Typical ranges were 0.04-9.2, 0.01-40, 0.001-1, or 0.01-3.2 ng x g(-1) dry weight for total PCBs, DDTs, HCHs, or HCB, respectively. These compounds exhibited a high dependence from the soil total organic carbon (TOC), showing high coefficients in the log(OC) versus log(TOC) correlations. The slopes of the curve fitted straight lines were, in turn, highly correlated to the log-transformed octanol-air coefficients of the compounds. This overall OC distribution points to steady-state conditions for the concentrations of these compounds in these mountain soils, in equilibrium with TOC. The equilibrium conditions are reached, despite the restrictions to convective air movement associated to the permanent atmospheric inversion layer at these latitudes. In addition, the log-transformed TOC-normalized concentrations of most PCBs, HCB, and pentachlorobenzene exhibit a good correlation with the reciprocal of average annual atmospheric temperatures also showing a temperature dependence for their distribution in the high mountain system. The calculated pseudo-enthalpies for this dependence, 120-160 kJ x mol(-1), exhibit higher values than those of octanol-air phase change calculated from laboratory experiments in previous studies, 66-93 kJ x mol(-1). The difference suggests a higher affinity of OC to soils than that corresponding to simple adsorption mechanisms.