Atmosphere

The Environmental Protection Agency has expressed fears that even short lived halocarbons may have a significant detrimental effect on the global atmosphere, as well as concerns about our relative lack of understanding of the environmental effects of these compounds2. Several chlorinated solvents are listed by the U. S. Environmental Protection Agency (U.S. EPA) as a hazardous air pollutant (HAP) under the U.S. Clean Air Act. However, various environmental NGOs and organisations maintain that current regulation of chlorinated solvent disposal is inadequate - for example, chlorinated solvents are not regulated under the Montreal Protocol despite evidence that they may contribute to ozone depletion.

Photochemical Smog

TCE and PBRC have both been linked to photochemical smog - both used in textiles industry

Global Warming

Dichloromethane has a Global Warming Potential (GWP) ten times greater than that of carbon dioxide, whilst trichloromethane has a GWP 30 times greater. At the time of writing the GWPs of tetrachloroethene and trichloroethene are not known, but are expected to be comparable to those for DCM and TCM.

Acid Rain

In the lower atmosphere degradation of chlorinated solvents is initiated by a reaction with the hydroxyl radical, and forms a variety of products including hydrochloric acid, formic acid, and phosgene (the colourless gas infamous for its use as a chemical weapon during World War One). These compounds dissolve in cloud and rain water and are ultimately deposited from the atmosphere in acid rain and snow.

Further, trichloroacetic acid (TCA) can be formed as a minor product in the atmospheric deg-radation of some chlorinated solvents. Studies have shown that TCA is broadly distributed in precipitation, surface water and soil on a global scale. Since the observed levels in soil in some areas have been found to exceed the accepted 'safe' levels (2.4 μg/kg for terrestrial organisms) the European Commission instructed producers of the relevant solvents to carry out extensive studies of the origin and fate of environmental TCA. Although the results of these studies suggest that TCA levels in soils could not be explained by precipitation alone, the European Union Risk Assessment on nevertheless concluded that “it is considered unlikely that depo-sition of TCA from the atmosphere will by itself lead to levels of TCA in soil that pose a risk for ter-restrial organisms”.

Biosphere

Humans

The Reference Dose (an estimate of the maximum level of continuous exposure to the human population which is unlikely to pose any significant risk of detrimental effects (excluding the risk of cancer of the course of a lifetime) for DCM is 0.06 milligrams per kilogram of body weight per day. DCM and other chlorinated solvents can have a devastating impact on human health. Case studies of DCM poisoning during paint stripping operations have shown that overexposure can be fatal to humans. Acute inhalation exposure can cause short term damage to the central nervous system including detriment to visual, auditory, and psychomotor functions, and irritation to the nose and throat. The major effects of chronic inhalation of DCM are also effects on the nervous system, including headaches, nausea, memory loss, and possibly dizziness. There is currently a lack of research indicating whether there may be developmental or reproductive effects in humans, although animal studies have previously shown that if DCM passes through the placental barrier there is a high risk of skeletal variations and/or lower fetal body weight. DCM is also considered a probable human carcinogen. Although research in this area is incomplete, animal studies have shown a sharp increase in liver and lung cancer and in mammary gland tumors following exposure to DCM. The US Environmental Protection Agency has concluded that, by a weight of evidence evaluation, 'dichloromethane is [and should be treated as] carcinogenic by a mutagenic mode of action'.

Animals

Tests have shown that acute exposure to DCM causes moderate acute toxicity from oral/inhalation exposure in many animals. Chronic exposure can lead to problems with the liver, kidneys, nervous and cardiovascular systems of a variety of animals.

Plants

The No Observed Effect Concentration (NOEC) for the most sensitive species of plants was 46 μg/m

Groundwater

IN a public health statement, the Agency for Toxic Substances and Disease Registry admitted that we do not know precisely how long chlorinated solvents may remain in the soil. What we do know, however, is that chlorinated solvents are a 'big deal' in groundwater - in fact, they are the most frequently detected groundwater contaminant in the USA. Chlorinated solvent pollution also affect surface water - although these chemicals tend to volatilise, and are extensively diluted in big rivers, the environmental and drinking water quality standards are very low in comparison to their solubility. TCE and TeCE are amongst the common contaminants and are particularly tricky to deal with due to the fact that their biodegradation pathways start off with reductive dechlorination to vinyl chloride, which in an anaerobic environment works fine. But then the process often gets stuck at vinyl chloride as that is typically oxidised in groundwater. (With VC being far more carcinogenic than TCE and TeCE this is a problem.) TCE is probably the prevalent groundwater contaminant these days.

Marine Environment

Chlorinated solvents are generally highly volatile and only sparingly soluble in water. Even if traces of solvents are briefly present in aqueous waste streams, they volatilise from rivers and lakes with a half-life of about a month or less, unless they are trapped in groundwater. Nevertheless, presence of chlorinated solvents is a concern due to its potential impact on marine life...