Effects of Color Dye on Plants

Adding food coloring to water in a flower vase is a good way to see the effect of dye on plants.

Plants feed on the nutrients and moisture in the soil, so dye from consumer products that ends up in the natural environment may have an impact on plant life. Usually, the effect is harmless, because most dyes used today are plant- or animal-based and non-toxic. However, this is not always the case.

Transpiration

A common science experiment for grade-school children is to place cut flowers in a vase with water and food coloring. As water evaporates from tiny pores on the flowers, the stems draw in water from the bottom of the vase. That colored water travels up the stem and into the leaves and flowers. As it does, the flowers change color because of the dye in the water. However, because food coloring is harmless, the effect of these dyes on cut plants is only cosmetic.

Growing Plants

Adding non-toxic dyes to the water and soil on which growing potted plants feed will have a similar effect as the transpiration experiment. In the natural environment, this is much more difficult to do because you would have to use very large amounts of dyes.

Synthetic Dyes

Some sources of non-food-coloring dye that may end up in plants growing outside is from colored mulch and products added to compost heaps. These include synthetic dyes. While these dyes typically are not present in high enough levels to alter the appearance of plants, some contain heavy metals that end up in the soil and are absorbed by plants.

Harmful Substances in Dyes

Heavy metals are usually not present in levels significant enough to have an effect on plant life. That's because plant roots have a hard time absorbing metals that are not soluble in water, according to a 1978 article published in Environmental Health Perspectives. At the same time, many plants have the ability to collect high toxic levels of chemicals without being harmed. That's why plants are often used to draw chemicals out of polluted sites, said Leon Kochian, director of the U.S. Plant, Soil, and Nutrient Laboratory at Cornell University, in a 2007 article.

Aquatic Plants

Like all plants, submerged aquatic plants need sunlight to survive. Dyes, whether natural or synthetic, can harm submerged aquatic plants by preventing sunlight from reaching them because of increased water opacity. It's the same effect that occurs during phytoplankton blooms or when falling leaves cover the water's surface.

References

• MadSciNetwork: Coloring Flowers
• John Shelley's Garden Center and Nursery: Dyed Mulch
• Pub Med Central: Soil and Plant Factors Influencing Heavy Metal Accumulation