Soil toxicities & pollution (ASK Advice)

Pollution: we've all seen news of the threat it can pose to clear air and clean water when it's left unchecked. But what about soil? Read on to learn about the toxic elements and effects of pollution that can be detrimental to soil health.

Some soil elements that can cause toxicities are actually essential plant nutrients, like micronutrients Boron, Chloride, and Copper. Plants need them in adequate amounts to thrive, but sometimes you can have too much of a good thing. Click here to learn about when more isn't always better when it comes to soil nutrients. While toxic levels of these elements can occur naturally, the most common cause is over-application of fertilizers (or copper-based pesticides). Be sure to check your yearly soil test results to avoid toxic levels!

Symptoms of Boron toxicity on rose leaves. Image: Malcolm Manners 

Besides plant nutrients, other soil elements can be safe at low levels but not low levels. A common example is aluminum, which can reach toxic levels in high acidity (low pH) soil conditions. While aluminum is a naturally ocurring element, acidity can be often caused by human activities such as excessive use of ammonium fertilizers, acid rain due to atmospheric pollution, or drainage from mining sites. Some plants can tolerate soil aluminum levels up to 5 ppm, while others are susceptible can be affected by 2 ppm or more. The main symptoms of aluminum toxicity in plants are stunted root growth and pale/yellow leaves. Aluminum can also block plant uptake of phosphorus, calcium, and magnesium and cause deficiencies of these nutrients.

Removal of heavy metal contamination from a former mining site in Montana. Image: US Forest Service - Northern Region

Other elements are always toxic: heavy metals such as arsenic, cadmium, and lead that are detrimental to humans and plants alike. Since your plants don't need these elements, we don't routinely test for them or intentionally add them to soil. They are naturally present in some soils, but tend to reach concerning levels due to pollution and wastes from mining, power plants, manufacturing, and others. People living or working on land with a histoy of industrial activity can opt for specialized testing to make sure their soil isn't contaminated with these dangerous elements. Plants can show all kinds of symptoms depending on exposure levels, such as chlorosis, deformed leaves, and stunted growth. 

Fertile soil is precious. Many causes of pollution and soil contamination might be beyond your control, but within your own yard you can use fertilizers and pesticides responsibly to avoid nutrient toxicities and maintain balance of essential soil nutrients.