# How to Calculate Distribution Coefficient

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Purchase bulbs, seeds and flowering plants to brighten and enhance your home and garden and give special attention to the quality of the soil in which these items will be planted. Understand that the content and quality of soil and how it impacts the environment is one of the responsibilities of the Environmental Protection Agency. They are instrumental in assessing and screening substances for existence of contaminants. One soil test assess the mobility of organic soil contaminants, within this test soil organic carbon-water partitioning coefficient (Koc) is used to derive the distribution coefficient (Kd), where Kd (L/kg) is the ratio of a chemical's sorbed concentration (mg/kg) to the dissolved concentration (mg/L).

### Things You'll Need

• Soil test kit
• Understand the components. Recognize the two primary components are sorbed concentration and dissolved concentration. Sorbed concentration reflects the level at which solids are capable of absorbing other chemicals and dissolved concentration is that which if freely dissolved.

• Identify the formula. Soil absorbs all products and by-products to which it is exposed. For example, when you wash your car, soap and water are absorbed into the soil, along with the dirt and grease from the tires and engine. In this setting, utilizing the formula Kd equals absorbed concentrate (mg/kg) divided by dissolved concentrate (mg/L). In organic settings, such as a farm the soil retains the effects of rainwater, nutrients and naturally formed contaminants such as animal waste. In this scenario, find the distribution coefficient (Kd) by multiplying Koc (soil organic carbon-water) times foc (the mass fraction of soil organic carbon content).

• Calculate the Kd. Purchase a soil analysis kit from a local gardening store or a nursery. Perform the test and insert the appropriate values and compute Kd, recognizing that the higher Koc values indicate conditions of less mobile organic chemicals while lower Koc values correlate to mobile organic chemicals.

## References

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