What are the causes of soil pollution?

Physical pollution

This form of pollution alters the natural structure of the soil without necessarily introducing chemicals.

It can be found in the form of:

• Microplastics from waste, mulch, packaging or tires;
• Unsuitable fill containing rubble, metals or construction site waste;
• Soil compaction , preventing the circulation of air and water;
• Erosion and artificialization , reducing microbial life.

This type of pollution alters the biological functioning of the soil: water circulates less, roots breathe poorly, and earthworms disappear.

Biological pollution

Here, the contamination comes from microorganisms or pathogens.

Examples:

• Bacteria from wastewater or poorly decomposed compost;
• Pathogenic fungi (Fusarium, Pythium, etc.);
• Proliferation of invasive species or harmful organisms.

This type of pollution can threaten food safety, particularly for vegetable gardens or livestock farming areas.

Point source pollution and diffuse pollution

We also distinguish:

• Point pollution : localized (e.g., tank leak, industrial spill, former gas station).
• Diffuse pollution : spread over large areas (e.g., intensive use of pesticides, air pollution, metallic dust deposits).

Each type of pollution requires a specific analysis protocol. At Pouryère, we adapt our sampling and testing to the on-site situation to guarantee reliable interpretation.

Before any list, here are a few accessible explanations:

• Heavy metals : elements such as cadmium, arsenic, lead – toxic even in small doses, accumulating in organisms;
• PCB, PAH, BTEX, HCT : families of stable organic molecules, often derived from combustion or solvents, persistent in the environment;
• PFAS (Eternal Pollutants): very stable C-F molecules, difficult to degrade, therefore described as “eternal”.
• Pesticides & nitrates : mainly present on intensively cultivated land.

The following list presents the most common types of chemical pollutants found in soils:

• Heavy metals (arsenic, cadmium, lead, etc.);
• Total hydrocarbons (TCH);
• PAHs – polycyclic aromatic hydrocarbons;
• BTEX – benzene, toluene, ethylbenzene, xylenes;
• PCB – polychlorinated biphenyls;
• PFAS – per- and poly-fluoroalkyl substances (“perennial pollutants”);
• Pesticides & nitrates (eutrophicants).

Soil pollution doesn't stop at the boundaries of the land. It profoundly alters the functioning of ecosystems. The effects vary depending on the nature of the pollutants, but several major impacts are observed.

Disruption of soil biodiversity

Healthy soil is a reservoir of life: bacteria, fungi, nematodes, earthworms, insects.

• Exposure to heavy metals (lead, mercury, cadmium) reduces the density of microbial communities by more than 40% in some contaminated areas (source: INRAE, 2021).
• Pesticides affect mycorrhizal fungi, which are essential for the absorption of phosphorus and nitrogen by plants.

As a result, the soil loses its fertility and its capacity for natural regeneration.

Toxicity to plants and wildlife

Pollutants accumulate in plant tissues and then move up the food chain:

• Cadmium is absorbed by root vegetables (carrots, beets) and ends up in the human diet.
• Polycyclic aromatic hydrocarbons (PAHs) decrease seed germination and slow the growth of young shoots.
• Birds and mammals are indirectly exposed by ingesting contaminated invertebrates.

This phenomenon is called bioaccumulation , and it leads to chronic effects over several generations of species.

Weakening of ecosystems

Polluted soil becomes a hostile environment:

• Plant diversity is declining, and some species are disappearing. In industrial wastelands, one often finds monotonous vegetation (resistant grasses) but few varied plants.
• Natural habitats are deteriorating, reducing shelter for insects, amphibians and birds.
• Ecological resilience (the ability to regenerate after a shock) is weakened.

Example: in Lorraine, former mining areas still show almost sterile soils today despite the cessation of mining for 30 years (source: BRGM).

Risks to water quality

Soils act like a sponge. But when they are saturated with pollutants, these migrate into the water:

• Nitrates and phosphates are leached into rivers, causing eutrophication (proliferation of green algae) which suffocates aquatic life. In Brittany, this phenomenon affects entire beaches every summer (source: Ifremer).
• Pesticides are regularly detected in groundwater: in 2021, ANSES reported that 20% of drinking water intakes in France showed traces exceeding regulatory thresholds.
• Volatile organic compounds (VOCs) from petrochemical pollution migrate rapidly into groundwater, making the water unfit for consumption.

In summary: soil pollution is not limited to the soil. It disrupts underground life, contaminates plants, threatens wildlife, and permanently degrades water quality – creating a domino effect that impacts the entire ecosystem, including humans.

The eternal nature of certain pollutants

Some compounds, such as PFAS, are called "forever" pollutants because of their very high resistance to natural degradation. They accumulate in ecosystems and organisms without ever disappearing.

Risks to human health

Pollutants present in the soil do not remain inert. They pass into the air, water, and food:

• Heavy metals :
  • Lead is neurotoxic. ANSES reminds us that no threshold is risk-free, especially for children. In some industrial areas such as Saint-Laurent-le-Minier (Gard), concentrations exceed 1,000 mg/kg , or 10 times the reference values;
  • Cadmium causes kidney and bone problems. The EFSA (European Food Safety Authority) considers an intake of 2.5 µg/kg of body weight/week to be critical.
• Polycyclic aromatic hydrocarbons (PAHs) : some, such as benzo[a]pyrene, are classified as known carcinogens (IARC Group 1) . They are found near former coking plants and petrochemical sites.
• PFAS (perennial pollutants): endocrine disruptors. They increase the risk of kidney and testicular cancers and disrupt fertility (source: Public Health France, 2022).

• In France, nearly 7% of the sites listed in the BASOL database present a direct health risk to exposed populations.

Risks to agriculture and food

When the soil is contaminated, agricultural production becomes dangerous:

• Root vegetables (carrots, potatoes) concentrate more heavy metals than leafy vegetables.
• In Île-de-France, urban vegetable gardens installed on former wastelands have revealed lead levels exceeding 300 mg/kg , rendering the crops unfit for consumption (source: BRGM, 2021).
• Excess nitrates in agricultural soils migrate into forage crops. When ingested by cattle, they cause methemoglobinemia (“brown blood disease”), which reduces oxygen transport in the blood.

This transfer of pollutants to the human diet is called the food chain of exposure .

Risks to the environment and ecosystems

• Soil fertility loss : in areas where PAHs exceed 100 mg/kg , microbial activity drops by more than 60% (INRAE, 2020).
• Death of soil fauna : earthworms, essential for aeration and agronomic balance, die as soon as copper levels exceed 150 mg/kg .
• Migration to waterways : nitrates and pesticides are reaching rivers. In 2021, ANSES detected traces of pesticides in 92% of French waterways .
• Unstable ecosystems : degraded soil can no longer store carbon or regulate water. This increases the risk of floods and droughts.

In summary: soil pollution represents a triple danger .

1. For men , with serious pathologies (cancers, chronic diseases).
2. For agriculture , with direct contamination of the food chain.
3. For the environment , with sterilized soils and weakened ecosystems.