Soil pollutants: what are they, where do they come from, and how can they be detected?

Heavy metals

The main inorganic pollutants are heavy metals such as lead, zinc, cadmium, arsenic, mercury, nickel, and chromium. They can occur naturally, but only in trace amounts, in very small quantities. Industries such as metallurgy, waste incineration, and paint manufacturing can produce them.

Some of these compounds are considered carcinogenic by the IARC. This is the case for cadmium and its derivatives. Lead is a probable carcinogen, while methylmercury is classified as a possible carcinogen. These metals enter the body through inhalation, skin exposure, or ingestion of contaminated water or food. Thus, foods with the highest cadmium content include shellfish, offal, biscuits, and chocolate.

Fluorides, chlorides and sulfates

Alkaline and alkaline earth fluorides, such as sodium fluoride, are toxic if ingested and can cause skin and eye irritation. They are used in metallurgy, metal pickling, wood preservation, and pharmaceutical manufacturing.

Chlorides are produced by chemical processes, oil wells, or in water treatment. They can be harmful in high doses, particularly for people with kidney or cardiovascular disease.

Finally, sulfates are used in shampoos, cosmetics, and detergents. They are what give these products their foaming and cleansing power, as well as their texture. They can irritate the skin over time and are air pollutants.

The impacts on human health

Most pollutants cause both short- and long-term effects. For example, exposure to VOCs or BTEX can lead to eye or skin irritation. At repeated doses, some pollutants are considered carcinogenic by the International Agency for Research on Cancer (IARC). They are classified in Group 1, such as benzene, benzo[a]pyrene, butadiene, formaldehyde, and diesel particulate matter.

Some heavy metals, such as cadmium, contribute to osteoporosis, increase the risk of bronchitis, and impair kidney function. This compound is also classified as a known carcinogen (Group 1) by the IARC.

Impacts on plants, animals and microorganisms

Most of the aforementioned soil pollutants are harmful to the environment and biodiversity. Soils are destroyed and lose their fertility, preventing any plant from growing normally. Plant growth is stunted, and groundwater and waterways are also contaminated.

Persistent effects (residual and bioaccumulative pollutants)

Some soil pollutants, such as PFAS, have a very long lifespan, sometimes lasting thousands of years. This is why they are called eternal pollutants. Persistent organic pollutants (or POPs) are characterized by several elements:

• The compounds degrade slowly and are persistent.
• They are bioaccumulative: that is to say, animals, humans and plants accumulate the substance over time if exposure persists.
• Exposure is toxic and can cause adverse health effects.
• They can move over long distances, far from the rejection points.

They can be produced intentionally: pesticides or industrial uses. Or non-industrially, for example through the open-air combustion of waste and biomass (forest fires, etc.).

Soil pollutants cannot necessarily be detected with the naked eye, but certain signs can nevertheless alert you.

Visible symptoms (plants, color, smells…)

If plants struggle to grow in your garden, or if they are stunted or yellowing, these are early warning signs. Rust-stained soil, yellowish, blackish, or greenish patches can indicate the presence of heavy metals or hydrocarbons.

Finally, foul or rotten odors are a sign of excessive moisture and mold, but not necessarily of harmful pollutants.

Laboratory analysis: a reliable and comprehensive method

Laboratory analysis is the most reliable and comprehensive method, provided the correct chemical compounds are sought. It is carried out in several stages:

• First, several soil samples will be taken from your land by a professional.
• The analysis of said samples in the laboratory to search for possible pollutants and determine their concentration level.
• Obtaining the results and interpreting them.
• The implementation of corrective actions and remediation if necessary.

Quick kits or tests: how good are they?

Rapid tests are often very limited and unreliable. It's best to purchase a complete kit. You collect the samples yourself, but the soil samples are sent to a laboratory for analysis. A few weeks later, you receive a detailed report of the results with interpretation. Pouryère offers this type of service through several dedicated kits for analyzing pollutants in your soil: analysis of heavy metals (arsenic, cadmium, chromium, copper, nickel, etc.), soil pollutants (HCT, PAHs, heavy metals), pesticides (trinitrogens, triazines, etc.), or PFAS such as PFOS or PFOA.

National databases (BASIAS, BASOL, SIS…)

National databases exist that list areas with polluted soil. One example is the Soil Information Sectors (SIS). This is an online map that allows users to enter a region, department, and municipality to obtain a list of affected areas.

BASOL is a database that lists polluted sites and soils that may require intervention by public authorities for remediation or prevention. BASIAS is also a national database that describes industrial sites, abandoned or active, that are likely to cause environmental pollution. You can consult it for an initial investigation. If your property is located in an area listed in BASOL, more detailed research is necessary.

Regulatory thresholds

Several reference standards offer limit values ​​for soil pollutants such as the NF U 44-551 standard which concerns crops, the decree of 12/12/2014 (ISDI - Inert waste storage facility) or the decree of 20/06/2023 which concerns PFAS or eternal pollutants.

Below are some of these values:

• The total lead analyzed in soil with or without fertilizer input must not exceed 100 mg/kg of dry matter.
• 300 mg/kg for total zinc.
• 1000 mg/kg of dry matter for sulfates present in inert waste and 1 mg/kg of dry waste for PCBs.
• Finally, for PFAS, measurements are taken in wastewater discharges. The maximum measurement for PFOA is 100 ng/liter, just as for PFOS.

What to do in case of exceeding the limit?

If the pollution level exceeds the limit, do not consume food products from the affected crops. Do not drink water from contaminated wells or groundwater. There is also a remediation obligation stipulated in Article L. 556-3 of the Environmental Code. In this context, the Prefect can order the execution of remediation work at the expense of the party responsible for the pollution: the last operator of the site, the producer, or the holder of the waste. It is possible to be held liable even if you are not the source of the pollution, particularly if it is proven that nothing was done to limit or contain it.

Precautions to take

Do not consume fruits, vegetables, or eggs produced by your chickens, as they feed on organisms living in the polluted soil. If your property contains pools of pollutants or an area of ​​inert waste, do not enter that area. Until a remediation company arrives, cordon it off with barriers to prevent anyone from entering.

If your soil contains pollutants, using a company specializing in remediation is essential.

Avoid exposure (barriers, mulching, usage restrictions)

The first thing to do is avoid exposure to pollution. This starts with restricting access through barriers and signage, and informing your family and friends. Also, keep your pets away.

Mulching is also a useful technique for preventing the dispersal of the most volatile chemical compounds. Certain plants are also considered to have pollution-reducing properties, such as red fescue, marsh sweetgrass, water hyacinth, and red clover. However, they may not be effective if you are dealing with deep-seated and long-standing pollution.

Pollution control: bioremediation, phytoextraction, containment…

Various pollution control techniques can be implemented by professionals:

● Bioremediation involves introducing specific microorganisms to eliminate waste. This is the case with certain bacteria and fungi. However, this technique has variable effectiveness, particularly against heavy metals such as cadmium or lead.

● With phytoextraction, plants accumulate pollutants in their harvestable aerial parts and reduce the concentration of harmful elements in the soil. There are so-called hyperaccumulator plants, often exotic, such as the tree Pycnandra acuminata or the shrub Grevillea exul, a species endemic to New Caledonia.

● The aim of containment is to isolate pollutants and prevent them from contaminating other spaces.

● There are a multitude of other techniques applied depending on the nature and extent of the pollution, such as chemical soil washing or particle size sorting.

Professional guidance

Any technique for removing soil pollutants requires the intervention of a professional. Only a professional will know which technique(s) to use and the best way to proceed. Even if you have a precise diagnosis of the pollutants present, do not undertake any remediation activity, even a natural one, without expert advice.

Solutions for individuals, farmers, communities and businesses

Each soil analysis kit is specialized and pursues a specific purpose:

• AGROKIT for agronomic soil analysis.
• POLLUKIT for pollutants.
• PESTIKIT for pesticide detection.
• PFASKIT for PFAS.
• METKIT for soil metals.
• SOLKIT for the complete health status of the soil (agronomic analysis, detection of pollutants and metals).
• ISDIKIT is aimed at construction professionals.