Solvents are indispensable in chemistry. Not only do they facilitate the dissipation of other substances (especially solids) into a more fluid form, but they also allow us to create the different concentrations necessary for precise reactions.
As well as being essential to chemistry and chemical manufacturing, solvents are used in food preparations and other daily activities. For example, when you prepare coffee for breakfast, hot water is your solvent to dissolve the coffee granules.
Solvents are everywhere, from the air we breathe (nitrogen) to the blood that flows in our veins (the red blood corpuscles themselves act as ‘solvents’ that carry oxygen and carbon dioxide).
Most solvents in nature are not toxic to organisms like oceans and the atmosphere. In fact, they actually support biological processes and make it possible for organisms to thrive. These large-scale, planetary solvents serve as the abiotic components of biomes.
However, many solvents used in industry are toxic and hazardous to the environment. Using safer solvents in chemistry will therefore help to solve many of our current environmental problems.
In this post:
What are solvents in chemistry?
The definition of a solvent in chemistry is a substance that can dissolve other substances or solutes without chemically reacting with them. It can be solid, gas, or liquid.
As a rule of thumb, solvents are also proportionally greater than solutes. Together, solvents and solutes form solutions, and therefore are technically interchangeable.
For example, air is a solution of oxygen (21%) and other gases (1%) dissolved in nitrogen (78%). Nitrogen is currently the solvent in the atmosphere because it’s the dominant component in terms of proportional mass and volume. However, it’s possible that in the future oxygen will become the dominant component and thus act as the solvent. 
On earth, the most commonly-used solvent is water. Its abundance and polarity make it a universal solvent because it can dissolve virtually all inorganic salts and most organic compounds.
Meanwhile, most of the solvents commonly used in the chemical industry are hazardous both to humans and the environment in general. Aside from water, some of the most common solvents used in chemistry and chemical manufacturing are varieties of the following:
- Alcohols
- Ketones
- Amide
- Esters
- Ethers
- Amine
- Nitriles
- Toluene
- Xylene
- Halogenated solvents
- Sulphur-containing solvents
Some of these industrial solvents are carcinogenic. All of them are toxic and potentially lethal at certain concentrations.
What are safe solvents
Safe solvents are those that do not pose any danger to human health, other organisms and the environment in general. They must not contain heavy metals and should be non-toxic, non-flammable (or at least have a high flashpoint), non-irritant, non-carcinogenic and naturally degradable over a relatively short period of time.
Few substances used in industries have these characteristics, with water being the only exception. Some, like ethanol or ethyl alcohol, are non-carcinogenic and do not contain heavy metals, but they are flammable. 
Other solvents like amines may not be flammable and are easily degradable, but some of them are toxic. Aniline, for instance, can destroy haemoglobin and may cause cancer in those who are chronically exposed to it.
Meanwhile, perfluorinated alkanes are a group of solvents that are safe for both humans and the environment. They can even be used as a blood substitute to carry oxygen.
The safest solvent in industry is still water, which is a good alternative to toxic solvents. However, the solute must be replaced with a water-soluble substance. For example, many paint products use water as a solvent instead of toluene or acetone.
Why sustainable solvents are important
Sustainable solvents are mostly non-toxic and organic. They’re classed as sustainable because they have zero – or at least very minimal – negative impact on the environment.
These solvents do not produce long-term waste products that can enter the food chain. Some of them, like water, are abundant and easy to obtain.
Are solvents bad for the environment?
Most of the solvents used in industries are naturally degradable and therefore have a short-term impact on the environment. However, others – particularly those that contain heavy metals, benzene, and poisonous substances – can have long-term serious effects.
Sourcing alternative industrial solvents goes hand in hand with the quest for finding alternative solutes for manufacturing various products. These range from adhesives and paints to polymer materials like plastics. Generally speaking, the best way to move forward is to use non-toxic, easily degradable solvents.
The hazardous effect of organic solvents
Organic solvents include hydrocarbons (aliphatic and aromatic), alcohols, acetones, esters, and other substances that contain carbon-based compounds and functional groups. Many of them are volatile and can have a direct effect on the nervous system.
The majority are also irritants and can damage organic tissues, while some are carcinogens and mutagens. Other organic solvents can be biomagnified in the food chain and cause harm to various organisms.
How to store solvents safely
Different types of solvents may have specific storage instructions based on their toxicity, reactivity, volatility, and flashpoints.
Most need to be stored in sealed inert containers, while some need to be kept in a temperature-controlled storage room. Here are some of the best practices for storing solvents:
- Affix proper labels, including the type of hazard
- Use spill trays and other spill protection
- Store chemicals in well-ventilated areas
- Use fire-resistant metal cabinets for flammable solvents
- Do not mix incompatible materials
- Avoid stockpiling hazardous materials beyond the recommended time
- Use tightly sealed containers to prevent spillage and evaporation
- Never store solvents with food, especially in refrigerated facilities
- Don’t forget to always wear proper protective equipment like gloves and goggles
- Practise safe handling techniques and protocols when handling chemical solvents in storage
How do green chemistry practices reduce risk?
Green chemistry emphasises the use of sustainable feedstocks and non-hazardous solvents. Reducing hazardous materials at the source will also significantly reduce the risk of chemical accidents such as poisoning and chronic exposure.
