Soil pollution happens when soil contaminants exceed a certain threshold amount that could pose a risk to human health and ecosystem or are simply above the natural background levels.
Soil pollution can affect humans through inhalation, direct skin contact, the consumption of poisoned vegetables and fruits grown on contaminated ground, as well as the use of or contact with the poisoned groundwater below the soil that circulates back on the ground. Exposure to the toxic compounds generated as a result of soil pollution can lead to various medical conditions.
Over time, what may have started as tiny amounts can reach considerable concentrations depending on environmental conditions (including soil types) and degradability of the released contaminant, and resulting in soil poisoning.
For example, metals are not degradable and may accumulate and concentrate in surface soils over time. However, not all metals behave similarly. A few metals can infiltrate into deeper soils, especially if precipitation is high (arsenic is one such example), while many other metals will stick to surface soils and become adsorbed by soil particles.
If the potential for repeated releases of non-degradable or less degradable contaminants (such as metals, PCBs, perchlorate) exists in a certain area, for instance, close to your home, it is always prudent to evaluate and test the soil for pollution through accumulation over longer time.
The sources of soil pollution are not always in the close vicinity and could be located far from the polluted soil. In such situations, pollutants are transported by the wind (especially if they are in the form of fine specks of dust) or by groundwater and could travel long distances, depending on their property and particle dimension. The smaller the particle and the more soluble and less reactive the pollutant, the higher is its potential to travel over longer distances and pollute soil far away from the release source.
A typical soil pollution example is mercury (Hg), which was proven to travel very long distances by air and get deposed on land hundreds of miles away, even polluting the arctic pole areas. PCBs or various other metals can also travel as dust, especially in very fine dust form (such as mine tailings). Because of this fact, it is always prudent not to assume that your garden is safe simply because you could not identify any local cause of soil pollution.
Bare soil generates a higher health risk than vegetated soil. This is because the bare soil is more exposed to wind erosion and may generate poisoned dust (soil poisoning dirt or soil poisoning dust) that can enter homes, spread across crops and vegetation, and be directly inhaled by people. Additionally, if soil is vegetated and regularly irrigated, there is less risk of pollutants accumulating and concentrating in that soil, although the risk for groundwater impact becomes higher in that case. In general, it is prudent to keep the lawn adjacent to your home well vegetated and irrigated in order to reduce any health risks from soil poison.
Soil pollution may generate health effects long after the original exposure occurred. This is due to the cumulative effect of some pollutants if inhaled or otherwise collected in the human body over long periods of time. Specifically, this is true in the case of pollutants which are taken in by our bodies and retained there, instead of being eliminated. Such contaminants are known to bioaccumulate in human organisms (and animal organisms too, for that matter). Examples of such contaminants are organic salts of mercury (such as mono-, di- or tri-methyl mercury) or PCBs (polychlorinated biphenyls). Poisoned soil may affect you through inhalation, direct skin contact, poisoned vegetables, and fruits (if grown in the soil), as well as poisoned groundwater below the soil (if consumed).