Most dirty sectors transform bulk raw materials into semi-finished products, producing large volumes of waste residuals in the process. Examples are provided by metals smelters, pulp mills, sugar mills, and chemical processing facilities. Wages are often low in these areas, so poverty and dirty production will reveal a natural, if accidental, spatial correlation. Dirty industry should therefore have a tendency to locate in low-wage regions. 2 Industrial water pollution has traditionally been the first focus of regulation in developing countries.
Water pollution is also easier to measure than air pollution.
For both reasons, the available data are much more plentiful for water polluters.