Global issues in setting legal limits on soil metal contamination: A case study of Chile.

The establishment of legal limits for soil contamination with trace elements is a global issue that has not yet been resolved. However, the resolution of any global problem begins at the national level. In this vein, we present the case of Chile, the world's leading copper producer, where soil contamination by trace elements in mining areas has been severe. We evaluated the magnitude of the ecological and human health risks from exposure to arsenic (As), copper (Cu), zinc (Zn), and lead (Pb) in soils of the La Ligua and Petorca basins, two important mining areas in Chile. Contrary to what might be expected in soils affected by Cu mining activities, As was identified as the most hazardous element in the studied soils, both in terms of ecological and human health risks. On the other hand, Chile does not currently have specific legislation establishing legal limits on soil contamination with trace elements. Since Chile is geochemically similar to New Zealand, Mexico, and Italy, we used the limits of these three countries as benchmarks. We determined the background concentrations of As, Cu, Zn, and Pb in the soils of the two river basins under study and found that they tend to exceed the limits established by foreign laws. We also found that the differences in background elemental concentrations in the studied soils were primarily due to the varied lithology of soil-forming rocks. This means that absolute "one-limit-fits-all" values of element concentrations may not be adequate to regulate the level of soil contamination in areas affected by mining. As a fundamental first step, it is necessary to establish background soil concentrations of trace elements in each river basin in Chile. It is clear that Chile urgently needs to move from rubber-stamping foreign laws to the development of national legislation on soil metal contamination.

Chilean regulations on metal-polluted soils: The need to advance from adapting foreign laws towards developing sovereign legislation.

Chile as a major international Cu producer faces serious soil contamination issues in mining areas. Currently Chile does not have any specific law governing the maximum permissible concentrations of metals in soils to protect ecosystems and human health. Chile heavily relies on the use of environmental laws of 14 foreign countries; the choice of the country depends on the similarity of its environmental conditions with those in Chile. In this study, we used an online database to compare the similarity of Chilean rocks to those in foreign countries. Likewise, we performed soil sampling and determined the background concentrations of Cu, As, Pb, and Zn in soils of the Aconcagua basin, the largest river basin in the Valparaiso Region of central Chile. The results showed that geochemical patterns in Chile have the greatest resemblance to New Zealand, Mexico, and Italy. The background Cu concentration in the Aconcagua basin (134 mg kg-1) exceeded the legislated limits of New Zealand (100 mg kg-1) and Italy (120 mg kg-1), whereas the background Zn concentration (200 mg kg-1) exceeded the legislated limit of Italy (150 mg kg-1). Due to the elevated natural abundance of Cu and Zn in Chile, international laws should not be applied in Chile for the assessment of soil contamination. In addition, we assessed ecological risk using the results of our previous studies obtained by analyzing native field-contaminated soils of the Valparaiso region. In the Aconcagua basin, Cu posed high risk for plants in 11% of the samples, whereas As posed high risk for earthworms in 48% of the samples. We suggest that future studies are required to search for other organisms that can serve as biomarkers of metal toxicity because our previous studies were limited to plants and earthworms. Importantly, As posed high risk to human health in 25% of the samples in our study. There is a need for future studies to demonstrate empirically an association between soil As and children's blood As in order to establish the national threshold values of soil As to protect human health. We conclude that there is an urgent need in Chile to advance from the current approach of adapting foreign laws to developing Chilean sovereign environmental legislation.