Contaminants and Urban Soil

In recent decades, urban gardens have become a popular option for people who want to grow their own produce at home. However, for those wanting to start an urban garden on a non-residential urban property such as a school yard, commercial area, or vacant lot, there is a high chance that the soils on that site are potentially contaminated with various chemicals. As a result, it is important for an urban gardener to have the soil at their potential site tested prior to planting the first few crops. Prior to the 1970’s environmental laws were almost nonexistent and it was not uncommon for hazardous chemicals to be dumped at any location where they were being used. Some of the common causes of soil contamination include unauthorized dumping, construction projects, and usage of lead based paints in nearby buildings.

The most common chemical contaminate in urban soils is lead with elevated levels of lead posing a significant health risk to young children who can ingest it either through playing in the soil or helping out in the garden. Once inside the body, ongoing exposure to lead can cause damage to the nervous system, and interfere with brain development along with creating other significant health problems. Aside from lead, other trace elements in the soil such as arsenic, cadmium, and copper can be elevated to unsafe levels by various past land uses. In addition to interaction with infected soil, another way consumers can unintentionally consume toxic chemicals is through plants. Plants absorb toxic chemicals in the soil through usage of various structures such as the roots, shoos, and leaves and pass the chemicals onto the people who consume the produce. Depending on the type of contamination, low levels of exposure may result in nausea, dizziness, fatigue, and headaches while higher exposure levels can result in neurological conditions and birth defects.

In order to avoid the negative aspects of contaminated soils, there are a number of steps that a person can follow. When selecting a potential site, if plants are growing abundantly on the site and if the soil is reasonably easy to dig through, than this is a positive sign that the soil can support crop growth. Also, the history of the site is important since any building built before 1979 and has old and peeling paint may be a hazard due to the lead in the paint.

If an urban gardener is concerned with the levels of chemicals in the soil at a potential site, they can have the soil samples tested at a lab. However, if the person cannot afford to have a lab test the soil samples, they can purchase a basic soil testing kit at a hardware store to provide some basic information on the fertility of the soil, but does not provide any information on soil contaminates. If the results from the lab test show that the soil at a particular urban site is contaminated there are a variety of things an urban gardener can do to live up to their food safety responsibilities. In areas where the levels of contamination are between 80 and 400 parts per million, the EPA recommends digging deeply and mixing large quantities of compost with the soil to dilute the levels of contamination and to avoid planting crops where the roots or foliage are consumed. In areas where contamination levels are higher than 400 parts per million, one option would be to hire a professional to safely remove the contaminated soil and replace it with clean soil. While this is a costly option, a cheaper option is to use raised beds for planting food crops. With this option, a piece of sheet fabric is laid down on the bottom of the bed before adding a layer of topsoil. The purpose of the fabric is to allow moisture through but prevents the roots from contacting the contaminated soil below.

One thought on “Contaminants and Urban Soil

  1. As an up and coming urban farmer, the topic of soil contamination is particularly interesting to me. I believe that its important to conduct soil tests before planting for public safety. Lead is the most common contaminant in urban soils. Based off UC’s agriculture and natural resource department, if the concentration of lead in the soil is <100 ppm then it is considered low risk and crops can be planted directly into the soil without restrictions. However is it exceeds 100 ppm it is labeled as moderate risk with raised beds and containers a recommended option along with the mixture of compost to dilute contaminant concentration. In addition, planting root crops should be limited. If the concentration of lead in the soil is higher than 1,200 ppm then it is considered high risk with raised beds and containers highly recommended. The selection of crops would be limited with root crops not encouraged. Yet as mentioned it is important to note the past history of the land to understand the current state of the contaminants found.

    To build upon the how to mitigate soil contaminants especially lead, remediation strategies include: digging thoroughly through the soil to mix and dilute the concentration of contaminants, maintaining soil pH around 7 to make heavy metals less available for plant absorption, and introducing organic matter after with each planting. Furthermore, adding and mixing Biochar with the soil can bind heavy metals to it and also has other benefits such as water retention. Activated charcoal can also be added to the soil to absorb pesticides and herbicides but may make the soil alkaline.

    These strategies may be utilized and incorporated together to mitigate the soil. Yet it is important to recognize that not all sites are appropriate for food production but my be used to grow trees, shrubs, wildflowers, and natives to beautify an area and provide a green space.

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