Soil is essential for the growth and development of plants and certain organisms by retaining moisture and nutrients. Microorganisms, known as soil biota, are highly important in maintaining soil health assisting with retention and deliverance of nutrients, maintaining soil structure, bioremediation of pollutants, erosion control, and more. The recognition of healthy soil as supporting and being sustained by living organisms is becoming increasingly important.
Volatile organic compounds (VOCs) is a harmful soil pollutant that slowly diffuses through the soil very slowly, sometimes taking years before the impact becomes noticeable and significant. The method of measuring VOCs in the soil is executed by evaporative loss measurement. It is determined VOCs at higher boiling points result in vapor, forming particulates.
Entry points come from a variety of sources such as wet or dry decomposition of the atmosphere, rain or smog, for example, dumping of waste, and petrochemical leakage. As VOCs enter the soil, they tend to be taken up by different soil components such as soil biota, soil organic content (SOC), mineral particles, water, and air. The distribution of a certain organic compound between components depends on the chemical affinity and the capacity of the compound. Distribution of VOCs is also not at an equilibrium since the rate of diffusing into the soil and its source are influencing factors.
The polarity, volatility, and chemical reactivity are factors in the distribution and movement of pollutants in soil and its residency time. Polar VOCs tend to dissolve soil water and removal of the compound depends in part on the soil’s water content and movement. The volatility is non-polar organics that can obstruct due to interfacial water layers and slow down the rate of movement due to its low solubility. The time within the soil depends also on their weight and Henry’s Law. In the absence of water or plentiful soil mineral surface adsorption sites, popular and non-polar VOCs of the same volatility are liable to have similar occupancy time. VOCs with both low volatility and water solubility are able to reside for possibly decades, and their removal depends on the chemical processes such as oxidation and hydrolysis assisted by soil biota. The most retained organic compounds are resistant to chemical and biological degradation, which are coincidentally harmful to soil biota and other lifeforms at very low concentrations.
Residency times of VOCs are also impacted by soil pH and temperature. Mineral and SOC content compromises chemically and topographically complex surfaces, interacting with VOCs and are highly variable. VOC movement in water or air is always governed by ground structural boundary conditions. A VOC can also become trapped under impermeable soil for many years. Theoretical calculations of residence time in soils suggest that even light, non-polar compounds reside in soils for many months, much longer than expected from their volatility. This can eventually be released as vapors through soil air with a tendency to escape into buildings at the sub-soil level. On the contrary, more polar VOCs tend to transport downwards towards the water, seriously contaminating groundwater.
For more information about the impact of VOCs in soil investigations and remediations, view the complete industry guide. To find out more about the products from ION science regarding soil remediation as well as gas and leak detection, view our products page. For more information about this article or if you have a question for us, contact ION Science today.