Whenever you wash dishes, laundry, or yourself. You send dirty water down the drain. What’s in it? And what effect does it have on the environment?

You have a variety of cleaning products to use. Most of them are either some kind of soap or some kind of detergent. They are necessary because, if the dirt includes any kind of oil or grease, water alone won’t clean it.

Nearly all compounds are either hydrophilic (water-loving) which means they will dissolve in water, or hydrophobic (water-hating), which means they will not mix with water.

Oil and water don’t mix. In order to clean it away, you need an emulsifier or surfactant. For all but the most technical purposes, we can use both words interchangeably. It disperses one liquid into another that does not naturally dissolve in it. Soap and detergent are the only ones we have to be concerned with.

Good cleaning results require a proper balance of three kinds of energy: chemical (provided by the soap or detergent), thermal (provided by hot or warm water except in detergents specially formulated to work in cold water), and mechanical energy. The agitator in a washing machine provides mechanical energy. So does rubbing hands together to make lather.

Soap and how it works

Soap is made from natural ingredients: fat and lye or some other alkali. In preindustrial times, it came from the ashes of burned plant material. The most common way to make soap is to mix the fat and lye and heat them. Humans have made soap since prehistoric times.

Professional soap makers arrived in the American colonies on the second ship to reach Jamestown in 1608, but until at least the middle of the 19th century, most soap was made at home.

Households necessarily used the same soap for bathing, shampooing, and all household cleaning tasks (laundry, dishes, etc.) It tended to be harsh and not especially good for skin or hair.

Both advances in chemistry and manufacturing techniques led to a fast-growing soap industry by the 1850s. Manufacturers could make a variety of different formulas, including milder soaps for personal cleansing.

Soap is the metallic salt of a fatty acid. The fatty acid can come either from plants or animals. The metals may be sodium or potassium. Soap is a straight chain carbon skeleton ending with a carboxylic acid group.

One end of the molecule (the carbon skeleton) is hydrophobic and the other (the acid group) hydrophilic. Mixing soap and water causes the soap molecules to form clusters (called micelles) with the carboxylic acid group on the outside, where it can dissolve in water.

The carbon chain on the inside never comes in contact with the water, but it attracts the oil and traps it inside. Water rinses the micelles away from whatever surface they’re on. The oil (and dirt and germs) goes down the drain with it.

Soap has one major disadvantage: The minerals in water react to the minerals in soap. They form a film that water won’t dissolve, such as the soap scum in your bathtub. It takes physical effort to remove it. The same film turns clothes gray and rough and reduces the luster of hair.

The amount of soap that reacts with minerals in the water is not available for cleaning—in addition to making visible deposits and making fabrics feel stiff. Soap is not a good laundry choice in areas with hard water. Soap scum can form even in soft water as a result of the dirtiness of the clothes.

Detergents and what’s in them

Detergents are made using petrochemicals, although they may have some natural ingredients. The surfactant in detergents has no carboxylic acid group but rather a sulfate or sulfonate group. They may contain aromatic rings.

As a surfactant, detergents generally work the same as soap, but not exactly the same way.

There are numerous chemical recipes for detergent: different kinds of surfactant plus additional ingredients. Most importantly, though, they don’t form a scum in hard water.

Germans developed detergents in 1916 because of a war-related shortage of soap-making fats. American manufacturers did not start making detergents until the 1930s.

Detergents became important products in the US only after the Second World War.

Again, a shortage of soap-making fats led to their growing use. The military also need a cleaning agent that would work in seawater and cold water, where soap is not satisfactory.

Since 1953, Americans buy more detergent than soap. Detergents all but replaced soap for laundry, dishwashing, and other household cleansers. Even some of the bars and liquids used for personal cleansing contain, or perhaps are, detergents.

The use of petrochemicals raises a number of environmental concerns, beginning with the pollution caused by extracting oil from the ground and transporting it to a factory where the chemicals are made.

Besides surfactants, detergents contain a number of other petrochemicals. The following is not a complete list, but no one product will contain everything on it.

• Builders to reduce water hardness and prevent removed soils from redepositing.
• Abrasives for smoothing or polishing.
• Acids or alkalis, but not both, because they neutralize each other. Acids help remove mineral buildup. Alkalis make surfactants and builders work more efficiently.
• Antimicrobial agents, which are unnecessary and contribute to resistant strains of microbes that are more difficult to kill.
• Antiredeposition agents, which like builders prevent removed soil from returning.
• Bleaches, which brighten and remove stains. Chlorine bleaches also disinfect.
• Optical brighteners to provide another means of making clothing look whiter or brighter
• Colorants, which may provide bluing action, but basically serve only to make one product look different from another.
• Fragrances to provide a pleasant odor and further distinguish one product from another.
• Foaming ingredients to make lather.

The lather does nothing to help the cleaning action of detergents. Lather is important for washing your skin with soap, because that’s what captures the dirt and germs that get washed down the drain when you rinse. The only reason for lather in detergents is that consumers think it’s what makes them effective!

The environmental impact of detergents

The Environmental Protection Agency summarizes the environmental impact of several of these ingredients. Some kinds of each have low toxicity and minimal environmental impact. Others raise serious concerns.

For example, among bleaches hydrogen peroxide and ozone have low toxicity and no toxic byproducts. Other bleaches are inherently toxic and also produce toxic byproducts.

My brief search for detergents without petrochemicals yielded a plethora of anti-corporate screeds. They hint that the government is involved in a general cover-up of how dangerous all commercial detergents are. Some time I’ll have to search lower in the search engine results pages and perhaps find reliable information.

Petroleum was the oil of choice when detergents were developed only because it was cheap and abundant. It stands to reason that it ought to be possible to make safe and effective detergent surfactants using natural oils and fats. Probably all the other ingredients in detergent, too.

The Environmental Protection Agency has introduced a “Design for the Environment” label. When a product bears the label it means that according to the best current scientific knowledge, it contains only those ingredients that pose the least concern among chemicals in their class.

The site contains an impressive list of both consumer and industrial products that have earned the label. I don’t suppose it necessarily means that they don’t contain petrochemicals.

Sources:
What is Soap? / World of Molecules
Soaps & Detergents / American Cleaning Institute
Key Characteristics of Laundry Detergent Ingredients / EPA
Labeled Products and Our Partners / EPA

Photo credits:
Water draining. Some rights reserved by flowr32.
Soap in action. Some rights reserved by Arlington County.
Dishwashing detergent. Public domain from Wikimedia Commons.
Design for the Environment logo. Public domain