Soil analysis of organic and inorganic contaminants in Goat Canyon (Canon De Los Laureles), at the U.S-Mexico border.

摘要

Los Laureles - Goat Canyon is a subwatershed located within the Tijuana River Watershed is presented. This canyon measures 1191 hectares (4.6 square miles), of which 90 percent is in Mexico, and the remainder is part of the Tijuana River National Estuary Research Reserve(TRNERR) in the U.S. In this canyon, as in most of the Mexican border region, the rapid human population growth has led to an unorganized urbanization established with squatter housing structures that lack potable water, sewage system, paved roads, and appropriate waste management. As a consequence, several opened solid waste dumpsites have been observed in the Mexican side of the canyon. These open dumpsites along with the lack of other public services are considered to contribute environmental contaminants that may affect human health and wildlife in the TRNERR. The objectives of this study were to (i) determine the presence and concentration of heavy metals in soil samples collected from Los Laureles/Goat Canyon, (ii) examine soil samples from Los Laureles/Goat Canyon using a non-targeted analysis to screen for the presence of organic pollutants including POPs, (iii) identify the possible sources of the soil contaminants in the canyon, (iv) obtain baseline data for future comparison with studies conducted on other contaminated soils, and (v) create a baseline data of the soil contaminants on the canyon that can be utilized in future research. This study utilized the X-Ray Fluorescence Spectrometry to screen for heavy metals in 24 composite soil samples. A comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC/ToF-MS) was used to screen for the presence of organic contaminants using a non-targeted analysis 9 composite soil samples. As results, 16 metals were detected, but only arsenic and cadmium were found to be above the EPA recommended levels (apply for cleaned Superfund sites). The soil concentrations of Cd found in this study are similar to previous studies done on the TRNERR, indicating .that the metal concentrations in this area havenot changed since the year 1997. With respect to the organic pollutants, this study identified 168 organic compounds, but there was only some scientific literature information for the only 30 compounds. Some organic contaminants such as benzothiazole (BT) and its derivative compounds seem to originate from rubber materials of the tires disposed at this canyon. Few pesticide related compounds such as hydroxylated biphenyl and benzyl benzoate were also found. Butylated hydroxyanisole (BHA), compound known by the state of California to have carcinogenic characteristics, and several phenolic compounds used as antioxidants were also detected in the screened soil samples. In addition, organic compounds that have may have endocrine disruptor characteristics such as octylphenols, galaxolide, musk ketone, bisphenol A (BPA), and triclosan (TCS), which are commonly used in household products were also detected in this study. Nonetheless, the origin of the majority of these compounds is unknown because they can come from a wide range of sources. For example, the several alkylated benzenes and PAHs found in this study might come from combustion or various forms of fuel. Only the parent PAHs, alkylated/partially saturated PAHs (semi-quantified), BPA, and TCS were quantified for this study. The PAHs concentrations were similar or lower than background concentrations around the world's soil, but the average concentration levels of BPA (209 ppb) and TCS (280 ppb) found in this canyon are noteworthy because they are higher or comparable to concentrations found in sewage sludge and soils amended with sewage sludge. This suggests that these contaminants may come from sewage due to the fact that the residents in this canyon lack a sewage system or a water treatment plant. Therefore, the concentration and verification of some of the organic compounds needs to be done, and further research measuring the concentrations and ecological effects of BPA, TCS, and other compounds related to municipal sewage in this canyon should be conducted.