Temperature dependence of the distribution of organochlorine compounds in the mosses of the Andean mountains

Abstract

Organochlorine compounds (OC), namely pentachlorobenzene, hexachlorobenzene, hexachlorocyclohexanes, polychlorobiphenyls (PCBs), and DDTs, have been studied in mosses distributed over three altitude gradients of the Andean mountains in Chile at 18°S (3200−4500 m above sea level), 37°S (345−1330 m), and 45°S (10−700 m). The observed concentrations range among the lowest values ever reported in remote sites, but they are still higher than those found in previously studied Antarctic areas. The log transformed OC concentrations show a significant linear dependence from reciprocal of temperature independently of the origin of the compounds, e.g. industrial, agricultural, or mixed. In the case of the more volatile OC these correlations involve variance percentages higher than 50%. This good agreement gives further ground to temperature as the driving factor for the retention of long-range transported OC in remote ecosystems, including those in the southern hemisphere such as the Andean mountains. In the context of the samples selected for study, the temperature dependences in the areas of similar latitude are related to altitude. Thus, all OC in the highest altitude gradient (18°S) and most compounds in the other two profiles (37°S and 45°S) exhibit higher concentrations with decreasing annual average temperature and thus increase with elevation above sea level. However, theoretical examination of the exponential equation relating OC concentrations to reciprocal of absolute temperatures shows that besides the temperature differences between highest and lowest elevation, the most relevant factor determining the OC concentration gradients is the lowest temperature value of each altitudinal series. That is, the point at highest elevation.