A Review on the Assessment of the Environmental Effects of Chlorinated Organic Solvents

Chlorinated solvents have been effectively used in various applications over many years. Manufacturers today support the applications listed below [1].

• Polyurethane foam blowing, • Formulation of coatings and adhesives, • Paint formulation and paint stripper manufacturing, • Formulation of aerosol products (perchloroethylene and methylene chloride only for certain applications in countries outside the European Union), • Metal cleaning / degreasing, • Dry cleaning, • Chemical processing industry, • Pharmaceutical manufacturing. The popularity of chlorinated solvents used in these industries stems from their low reactivity, non-flammability characteristics, ease of evaporation and strong solvency power [2]. Among the chlorinated solvent types commonly used in the sector, you can examine the fundamental chemical and physical properties of perchloroethylene, methylene chloride and trichloroethylene in Table 1. Volatile organic compounds (VOCs) are significant air and water pollutants that must increasingly be controlled under strict environmental regulations. Among these, chlorinated VOCs are used quite widely in the chemical industry in the production of herbicides, plastics and solvents. Uses outside the chemical industry include degreasing in the automotive and aerospace industries, dry cleaning in the textile industry and cleaning solvents in the electronics industry [3]. VOCs, which are used quite intensively in each sector, are a source of serious environmental problems and therefore VOC emissions are subject to stricter regulations [4]. Essentially, all substances both natural and man-made are toxic to some degree. Toxicity is defined as the ability of a substance to produce any harmful effect on a living organism at a particular level or frequency of exposure, whether inhaled, ingested or through direct skin or eye contact. Risk is determined by exposure and hazard. Thus, the potential risk of hazardous substances can be significantly reduced by correct use, such as through the use of engineering controls, respiratory masks, chemical goggles and other safety equipment.

Table 1. Chemical and physical properties of MC, TCE and PCE

Table 2. Summary of potential health effects of chlorinated solvents from acute exposure in humans

(a) For example; dizziness, pain, drowsiness. When these effects occur, personnel are provided with oxygen and moved to fresh air. (b) May cause irritation and pain; rinse thoroughly with pure water without soap. (c) All chlorinated solvents cause skin irritation on repeated exposure. [1] The most frequently encountered health problem in industries using high amounts of organic solvents is the necessity for employees to be continuously exposed to an atmosphere containing small amounts of solvent vapor as time goes on. The inhalation of small amounts of solvent vapors has no effect whatsoever, because, as indicated, these can be completely eliminated by the body. The amount of vapor that can be safely inhaled in this way varies according to the amount of solvent [5]. Commercial technologies exist for chlorinated VOC reduction. Among adsorption and separation technologies, activated carbon adsorption is widely used in industry due to its ease of use, low operating costs and efficient recovery of most chlorinated VOCs. However, activated carbon frequently encounters problems such as combustion and pore clogging. As a result, alternative adsorbents have drawn attention. Hydrophobic zeolites have been proven to be an advance in the control of chlorinated VOCs. Lee J. et al. obtained the adsorption equilibrium of seven chlorinated volatile organic compounds on mesoporous silicate (MCM-48) using a gravimetric technique. For comparison purposes, three organic adsorbents (activated carbon, activated carbon fiber and nonionic polymer resin, SP850) and three inorganic separators (DAY zeolite, mesoporous silicate MCM-41 and chromium-impregnated MCM-48) were used to investigate adsorption properties.

Trichloroethylene was also selected as a model compound of chlorinated volatile organic compounds. In this study, the aim was to develop efficient adsorption and catalytic decomposition of chlorinated VOCs on MCM-48 [3].

Adsorption of VOCs into selective solvents is an alternative technique for disposal to other processes (for example, thermal or catalytic incineration, adsorption on activated carbon, biological or membrane processes). Disposal of chlorinated species by incineration can lead to the formation of hydrochloric acid and dioxins. Additionally, thermal regeneration of sorbents can be problematic and may prevent the use of this technique. Waste gas cleaning using selective solvents shows an alternative and safe route for a reversible process and has been researched particularly by German researchers. The recyclable process allows for waste air cleaning and possible recovery of VOCs: This technique has been used for decades for other pollutants (for example, sulfur dioxide) with a series of organic substances. Selection of appropriate solvent for adsorption is usually made considering the following criteria: High absorption capacity, high selectivity relative to other gases, low toxicity and volatility are among these criteria. Although the formation of pollutant-solvent complexes has been demonstrated for sulfur dioxide in various solvents, previous research has shown that absorption of chlorinated VOCs should not result in the formation of such complexes. However, interactions between VOC and solvent molecules result in possible proximity or mutual repulsion and determine the solvent's adsorption capacity [4].

Figure 1. Detection frequencies of four solvents in groundwater at concentrations of 0.2 μg / L or above [9]

Chlorinated solvents have been widely misused and accidentally spilled since the 1940s in various industrial, military and domestic applications, as well as improper disposal practices, resulting in widespread groundwater and subsurface water pollution. In a study conducted by Betts K. et al., common chlorinated solvents, including 1,3 tetrachloroethene (PCE), trichloroethylene (TCE), carbon tetrachloride (CT), dichloromethane (DCM) and 1,1,1-trichloroethane (TCA)3, tend to form dense non-aqueous phase liquids (DNAPLs) that move gravitationally along interconnected fractures. The mass of significant chlorinated solvents in a fractured rocky area, using low permeability zones and return to water-bearing fractures, emphasized that it functioned as a long-term groundwater contamination source [6]. As indicated by Şimşir B. et al., in situ measurements showed that reductive dechlorination in sediment weakened chlorinated compounds before reaching the water column. Microcosms created with stream sediment or in situ incubated Bio-Sep beads decomposed C1-C3 chlorinated compounds into less chlorinated or harmless products. Microbiological and hydrogeological characterization showed that microbial processes at the limestone bedrock-sediment interface are important to prevent contaminants from reaching the water column, and emphasized the suitability of this critical zone environment for contaminant attenuation [6].

According to Betts K.'s research, using in situ redox manipulation technique, Bob Puis, senior soil research chemist at the EPA's National Risk Management Research Laboratory in Okla., stated that TCE, a solvent contaminant in groundwater, was destroyed.

In this technique, an in situ permeable treatment barrier blocks contaminants in groundwater and effectively prevents further spread of targeted chlorinated solvent contaminants in plumes [7]. Helt B. et al. developed a method in aqueous medium and at high temperature to reduce the environmental impacts of chlorinated organic compounds. They described the conversion of microgram amounts of chlorinated volatile organic compounds to CO2 and CH3Cl for C and Cl isotope ratio determinations. This method provided an analytical approach developed for using C and Cl isotope ratios in studies of biodegradation of chlorinated volatile organic compounds in the environment [8]. In conclusion, chlorinated solvents are not water-soluble, yet can still cause surface or groundwater contamination. Additionally, since chlorinated solvents are heavier than water, large spills tend to accumulate at low points, creating a concentrated source for continued contamination. Process water that comes into contact with chlorinated solvents will even contain some chlorinated solvents and must be treated as a hazardous waste stream. The main causes of groundwater and soil contamination are neglect and improper storage, transportation and disposal. Cleaning contaminated soil and water is difficult and costly. Therefore, it is necessary to avoid leaks and spills that could cause groundwater and soil contamination. Contaminated water must not be discharged to sewers or septic tanks or poured onto the ground. Emine Akbulut Chemical Engineer Sales and Marketing Manager Ef Kimya Tic. ve San. Ltd. Şti.  

References [1] Chlorınated Solvents Product Stewardshıp Manual, Olin Chlorinated Organics [2] Robert D. Morrison, Brian L. Murphy, and Richard E. Doherty, Chlorinated Solvents, Part 12, Page 260-272 [3] Lee J., Shim W., Suh S., 2003, Adsorption of Chlorinated Volatile Organic Compounds on MCM-48, American Chemical Society [4] Hadjoudj R., Monnier H., 2204, Absorption of Chlorinated VOCs in High-Boiling Solvents: Determination of Henry's Law Constants and Infinite Dilution Activity Coefficients, Ind. Eng. Chem. Res., Vol. 43, No. 9 [5] Lillian G., 1945, Using Organic Solvents Safely in Industry, Safety Research Institute, New York [6] Şimşir B., Yan J., Im J., Graves D., 2017, Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks, Environ. Sci. Technol. 2017, 51, 4821−4830 [7] Betts K., 1998, Novel Barrier Remediates Chlorinated Solvents, American Chemical Society [8] Holt B., Sturchio N., Abrajano N., 1997, Conversion of Chlorinated Volatile Organic Compounds to Carbon Dioxide and Methyl Chloride for Isotopic Analysis of Carbon and Chlorine, A n a l y t i c a l C h e m i s t r y , V o l . 6 9 [9] Moran M., Zogorski J., Squaillace, 2007, Chlorinated Solvents in Groundwater of the United States, Environmental Science Technology, Geological Survey, 1608 Mountain View Road, Rapid City, South Dakota 57702