Summary

The use of solvents in many applications (degreasing, cleaning, stripping, printing, painting, adhesives, pharmaceutical manufacturing) is a major concern. Several solvents are associated with adverse effects, both on the health and safety of workers (burns, cancer, dermatitis, encephalopathy, fetotoxicity, and polyneuritis) as well as on the environment and health of the general population (smog precursors, water pollution, and ozone layer). At the same time, more and more companies want to go green, i.e. to ensure that their activities and products are part of the sustainable development process. It is in this context that so-called green, ecological, biodegradable, and sustainable solvents have emerged. However, it is not always clear to what extent these "green solvents" are effectively environmentally friendly or safe for those exposed to these products. The objective of this study was therefore to produce a monograph presenting synthetic and critical knowledge on the health, safety, environmental, technical, regulatory, and normative aspects of solvents qualified as green.

A review of the scientific, technical, and commercial literature pertaining to green solvents has made it possible to classify them according to the origin of the raw materials used in their production. For example, we find solvents derived from carbohydrates, such as ethyl lactate and various alcohols, including butan-1-ol, lipid-derived solvents such as fatty acid methyl esters, or obtained from plants such as d-limonene extracted from citrus peels, or from lignocellulosic waste such as 2-methyltetrahydrofuran. In addition, new classes of green solvents have emerged, e.g. deep eutectic solvents (liquids obtained by mixing solids), ionic liquids (melted organic salts), switchable solvents (resulting from the bubbling of carbon dioxide in a liquid such as water), supercritical water and carbon dioxide (i.e. prepared at temperatures and under high pressures giving them organic solvent properties). In addition, water, in its normal liquid state, plays a role as a reaction medium, as well as in aqueous preparations used for industrial degreasing, coatings, adhesives and inks. Finally, a number of solvents are sometimes referred to as green, even if they come from petrochemistry, given their good environmental performance, e.g. parachlorotrifluoromethylbenzene, propylene carbonate, some siloxanes and polymeric solvents such as certain polyethylene glycols.

Some companies may be tempted by greenwashing or greening the solvents they produce or formulate. Greenwashing is a public relations exercise conducted by an organization to hide its polluting activities and attempt to present itself as an eco-responsible business. In addition, many manufacturers wishing to green their products have turned to environmental certification in the form of eco-friendly labels. These are intended to ensure impartiality in product evaluation and a guarantee of compliance with minimum criteria, while increasing transparency for consumers. In North America, for example, there are various certifications such as Green Seal, Greenguard, ECOLOGO. These labels generally target formulations such as paints, varnishes, cleaning products, adhesives, floor coverings or strippers. These labels largely focus on controlling the volatile organic compounds (VOCs) content. The Safer Choice label is based on a list of solvents considered more or less green according to various criteria, and categorized using a colour code. The Biopreferred standard aims to increase the use of bio-based products, i.e. products with a high content of recent organic carbon derived notably from forestry and agriculture. Various labels have been developed in Europe (EU Ecolabel, Nordic Ecolabelling), including a standard on bio-based solvents.

Many regulations on chemicals in the workplace or in the environment promote the substitution of conventional solvents and the use of green solvents. The Canadian Environmental Protection Act and, in Quebec, the Clean Air Regulation limit the emission of VOCs in various sectors. In Quebec, the substitution of hazardous materials emitted in the work environment is encouraged by the Regulation respecting occupational health and safety. The province of Ontario enacted the Toxics Reduction Act. In the United States, the Clean Air Act, which includes VOCs, and the Massachusetts’ Toxics Use Reduction Act apply. In Europe, the REACH regulation imposes the principle of substitution for a range of toxic substances and encourages their replacement with clean and sustainable products.

There are a variety of tools and sources of information to help replace traditional solvents and assist in the assessment and selection of green solvents, including the P2OASys spreadsheet file for all toxic substances from the Toxics Use Reduction Institute of Massachusetts, and the U.S. Environmental Protection Agency's PARIS III software for industrial solvents. There are also guides, documentation and selection tools specific to various applications such as in the pharmaceutical industry, chemical laboratories, paints, cleaners and degreasers.

Despite the proliferation of eco-labels and certifications, confusion remains to define what a green solvent is. A strict application of the green chemistry criteria means using a solvent that would be non-toxic to workers and the environment, derived from renewable resources and nonflammable. Since many of the green solvents used to replace traditional solvents are not safe for workers, it is justified to recommend that an analysis of the potential effects on workers' health and safety be undertaken in all substitution projects, to ensure that risks are not transferred from one risk category to another. To do this, the 9-step substitution method behind the Solub website must be applied whether faced with a supposedly green solvent or not.

It would be unwise for the authors of this report to make specific recommendations of green solvents applicable to all situations. However, certain categories of solvents need to be favored such as water, bio-based solvents such as fatty acid methyl esters, as well as those that meet a maximum of green chemistry criteria. Finally, in order to encourage the replacement of traditional solvents with green options in Quebec, legislators may refer to the State of Massachusetts’s Toxics Use Reduction Act, which, while restrictive for companies, provides resources to help them concretely carry out their plans to replace toxic substances.