Influence of altitude and age in the accumulation of organochlorine compounds in fish from high mountain lakes

Abstract

The analysis of hexachlorobenzene, hexachlorocyclohexanes, polychlorobiphenyls, and DDTs in muscle of fish from high mountain lakes shows that a proportion of their concentration variance depends on fish age and lake altitude. Interestingly, the magnitude of this share corresponds linearly with the log-transformed vapor pressure (Vp) of the organochlorine compounds (OC). Thus, the distributions of OC with Vp < 10-2.5 Pa are mostly determined by these two variables. Altitude gradients mainly respond to temperature differences, involving concentration increases of 25−150 times between 8.7 and −2.3 °C. The age effect encompasses concentration increments of 2.4−7.8 for average lake differences between 2 and 13 yr. However, both effects are independent since no correlation between fish age and lake altitude is observed. Fish liver concentrations exhibit the same pattern, but the correlations are only significant for age, suggesting that the temperature trend is more related to long-term accumulation than episodic intake. The temperature effect is independent from compound origin. In addition, the sites situated at highest altitude, those most distant from possible ground pollution sources, are the most polluted. The results can be explained by condensation effects such as those described for the latitudinal trends that support the global distillation theory. However, in the high altitude lakes a temperature-dependent amplification mechanism, probably related to low metabolism and respiration at low temperatures, enhances OC accumulation in fish beyond the increases predicted from theoretical condensation and solubilization enthalpies. The observed temperature dependence suggests that a general remobilization of OC accumulated in high mountain areas could take place as a consequence of the general warming of these areas anticipated in the climatic change studies.