nitroaromatics. Pink water is actually colorless at the time of generation, whereas red water can be colorless or a very pale red. The color is produced by photolytic reactions under the influence of sunlight. Despite the names, red and pink water are not necessarily different shades; the color depends mainly on the duration of solar exposure. If exposed long enough, "pink" water will become dark brown. Because of the toxicity of TNT, the discharge of pink water to the environment has been prohibited in the US and many other countries for decades, but ground contamination may exist in very old plants. However, RDX and tetryl contamination is usually considered more problematic, as TNT has very low soil mobility. Red water is significantly more toxic and as such it has always been considered hazardous waste. It has traditionally been disposed of by evaporation to dryness (as the toxic components are not volatile), followed by incineration. Much research has been conducted to develop better disposal processes. Ecological impact Because of its suitability in construction and demolition, TNT has become the most widely used explosive and thus its toxicity is the most characterized and reported. Residual TNT from manufacture, storage, and use can pollute water, soil, the atmosphere, and the biosphere. The concentration of TNT in contaminated soil can reach 50 g/kg of soil, where the highest concentrations can be found on or near the surface. In September 2001, the United States Environmental Protection Agency (USEPA) declared TNT a pollutant whose removal is a priority. The USEPA maintains that TNT levels in soil should not exceed 17.2 grams per kilogram of soil and 0.01 milligrams per litre of water. Aqueous solubility Dissolution is a measure of the rate that solid TNT in contact with water is dissolved. The relatively low aqueous solubility of TNT causes solid particles to be continuously released to the environment over extended periods of time. Studies have shown that TNT dissolves slower in saline water than in freshwater. However, when salinity is altered, TNT dissolves at the same speed. Because TNT is moderately soluble in water, it can migrate through subsurface soil, and cause groundwater contamination. Soil adsorption Adsorption is a measure of the distribution between soluble and sediment adsorbed contaminants following attainment of equilibrium. TNT and its transformation products are known to adsorb to surface soils and sediments, where they undergo reactive transformation or remained stored. The movement