Environ. Sci. Technol. 2002, 36, 1879-1885
Temperature and Organic Matter Dependence of the Distribution of Organochlorine Compounds in Mountain Soils from the Subtropical Atlantic (Teide, Tenerife Island) ALEJANDRA RIBES AND JOAN O. GRIMALT* Department of Environmental Chemistry, Institute of Chemical and Environmental Research (ICER-CSIC), Jordi Girona 18-26, 08034 Barcelona, Catalonia, Spain C A R L O S J . T O R R E S G A R C IÄ A A N D EMILIO CUEVAS Izan ˜ a Atmospheric Observatory, National Institute of Meteorology, La Marina 20, 38071 Santa Cruz de Tenerife, Canary Islands, Spain
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‚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 logtransformed 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 logtransformed 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‚mol-1, exhibit higher values than those of octanol-air phase change calculated from laboratory experiments in previous studies, 66-93 kJ‚mol-1. The difference suggests a higher affinity of OC to soils than that corresponding to simple adsorption mechanisms. * Corresponding author phone: 34 93 4006122; fax: 34 93 2045904; e-mail:
[email protected]. 10.1021/es010272h CCC: $22.00 Published on Web 03/23/2002
2002 American Chemical Society
Introduction Polychlorinated biphenyls (PCBs), DDTs, hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), and other organochlorine compounds (OCs) remain in the environment, despite their discontinued use in most countries as a consequence of their high chemical stability, hydrophobic properties, and low volatility. These properties also determine their selective accumulation in specific ecosystems such as those in cold areas. Thus, part of the OCs released in the northern temperate areas, where they were used most intensively, accumulated at high latitudes (1-3) or at high mountain sites (4). This transfer involves a reversal of the common pollutant dilution trend upon release into the environment. This mechanism, called the global distillation effect (3, 5, 6), encompasses the concentration of these compounds from diffuse pollution to environmental cold sites as a consequence of condensation. However, this mechanism, and its relevance for OC transfer, has only been considered in ecosystems at high latitudes (1-3) or, recently, in high mountains of temperate areas (4). A global understanding of the distribution pattern of these compounds also requires the inclusion of low latitude regions. In the present paper, a mountain system in the subtropical Atlantic Ocean (28°N 16°W; Teide, Tenerife, Canary Islands; Figure 1) is considered. This area is characterized by a stable temperature inversion year-round that separates air masses of lower altitude (below 1000 m) from the free troposphere (above 1800 m). These conditions result from the descent branch of the Hadley cell at this latitude. They involve a different meteorological situation from that in mountain systems of temperate areas (4) where the vertical structure of the atmosphere is less stable and changes depending on season and local weather episodes. The distribution patterns of PCBs, DDTs, HCHs, HCB, and pentachlorobenzene in the soils of this mountain system are considered. Soils constitute the main compartment for the accumulation of OC in the dry environments of these regions. To the best of our knowledge, this is the first study considering the distribution of OC in mountains of low latitude areas.
Materials and Methods Meteorological Data. The average atmospheric temperature profiles were obtained after summarizing the hour-to-hour long-term climatic records stored at Izan ˜ a (Spanish National Institute of Meteorology (INM)). Materials. Residue analysis n-hexane, dichloromethane, isooctane, methanol, and acetone were from Merck (Darmstadt, Germany). Anhydrous sodium sulfate for analysis and powdered copper (size
