Reviews of Environmental Contamination and Toxicology

Regulation of industrial discharges to the environment has been increased in the last few decades (Fisher 1994). In the European Union, this is leading to the establishment of Integrated Pollution Prevention and Control (IPPC) as the guiding principle in the authorization of pollutant discharge by industry. As part of this, pollutant discharges have to be monitored to prevent exceedence of the limits set by the licensing authority (Bigg 1994).

Mercury is one of the most studied environmental pollutants. Elemental mercury is spread very effectively from different sources and may be methylated in the environment. Methylmercury is more toxic, very persistent, and readily bioaccumulated, especially in aquatic food chains In most industrialized countries, actions have been taken to minimize contamination with heavy metals and other harmful substances. In many developing or recently industrialized countries, however, the pollution problem is much more complicated. There is an obvious lack of knowledge, legislation, governmental control, analytical capacity, and monitoring.

Metals are natural constituents of rocks, soils, sediments, and water. However, great changes have occurred regarding the global assessment of critical chemical substances after the Industrial Revolution, approximately 200 years ago, challenged those regulating systems that took millions of years to evolve. A clear example is the Gulf of Mexico, where the presence of metals in its coastal ecosystems answers to the introduction of pollutants by river inputs, among which two of the greatest deltaic systems of the world, i.e., the Mississippi River in the United States and the Grijalva Usumacinta Basin in Mexico, are prominent. Additionally, industrial and commercial activities that have developed in the giant harbor complexes of Brownsville, Corpus Christi, Houston, Galveston, and New Orleans in the U.S. and those of Tampico-Madero, Altamira, Veracruz, Coatzacoalcos-Minatitlan, Dos Bocas, and Ciudad del Carmen in Mexico have greatly contributed to the large volume of toxic wastes dumped into the waters of the Gulf, including a large variety of metals.

Polychlorinated diphenylethers (PCDEs), sometimes called chlorinated diphenyloxides, have a structure that resembles that of polychlorinated biphenyls (PCBs) (Fig 1.). The difference is the oxygen atom that connects the two phenyl rings and which is absent in the PCB structure. Although the numbering system of the PCDEs is identical to that of PCBs, the two compound classes are essentially different. Their widespread occurrence in the environment is mainly the result of their presence as impurities in chlorophenol preparations (Becker et al. 1991). The presence of PCDEs next to polychlorinated dibenzo-pdioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in commercially available chlorophenols of technical and analytical grade has been confirmed by infrared spectrometry and mass spectrometry (Becker et al. 1991).