Eco-Experts Answers Your Environmental Questions

Get help with detergent, home heating and flea control questions.

| January/February 2004

  • Caroline Blazovsky
  • Carol Steinfeld
  • Pete Nichols

Detergents in graywater 

Is graywater containing Wisk detergent safe for lawns and plants? The detergent, called Wisk Action with Colorhold, is labeled “biodegradable with no phosphorus and safe for septic systems.”
—Kitty Jansen Arena, Wisconsin  

Carol Steinfeld replies: 

Most soaps and detergents won’t kill plants outright. Some even feed them. However, some ingredients can clog plants’ “arteries.” Soaps emulsify soils, microbes, and liquids, detach them from surfaces, and act as a surface action agent (surfactant) to reduce water’s surface tension, making it “wetter.” Detergents go a step further, detaching and binding up particles so they can be washed away.

Many soaps contain sodium hydroxide. This increases the amount of sodium in the graywater, while the hydroxide raises the pH, or alkalinity. Sodium can inhibit water and nutrient transport in some plant cells and change the osmotic balance. In other words, sodium causes hypertension in plants, just as it can in humans.

Wisk only lists its ingredients in general terms, but it appears that it will not harm gardens irrigated with graywater. If you are planting salt-sensitive plants, look for potassium-based laundry soaps instead. Potassium is a fertilizer and a beneficial nutrient. Most liquid soaps are made with potassium hydroxide. Potassium hydroxide serves as an excellent grease remover; it works by turning grease into soap. Tri-potassium phosphate (TKP) is a powerful cleaner that is used on sewer pipes and automotive engines.

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