Titanium dioxide: known environmental impacts?

Titanium dioxide in the environment: an invisible threat?

The titanium dioxide is a metallic oxide found naturally in minerals such as ilmenite and rutile. It exists in crystalline forms such as anatase and rutile. Due to its unique properties, notably its bright whiteness and ability to protect against UV radiation, it is used in various industrial applications.

In nanometric form, TiO₂ offers higher performance, making it suited to applications such as cosmetics and paints. Unlike the micrometric form, nano-TiO₂ are known for their high chemical reactivity, which can lead to accumulation in ecosystems. When these particles are released into the environment, they can have harmful effects in water, soil, and air.

What is the impact of nano-TiO2 on aquatic ecosystems?

Nano-TiO2 particles entering surface and marine waters affect aquatic ecosystems. These reactive particles undergo physical, chemical, and biological transformations. These processes influence their behaviour and toxicity in aquatic environments. Studies show they accumulate in aquatic organisms such as phytoplankton, fish, and filter-feeding molluscs. This accumulation can affect organism health and food webs. Phytoplankton, an essential component of the marine food chain, absorbs nano-TiO2. Their UV-driven photoreactivity generates harmful oxidative stress.

Nano-TiO₂ can interact with heavy metals (Cu, Zn, Cd, As) and organic pollutants, increasing their toxicity to marine life. This interaction raises the bioaccumulation of these substances in marine organisms, disrupts the food chain, and poses a risk to human health through consumption of contaminated fish and shellfish. Research shows that exposure to TiO₂ at low concentrations (6.3 mg/L, half the maximum permitted level for UV filters in sunscreen) can cause the loss of symbiotic microalgae in corals, trigger bleaching, and impair reef health. These concentrations lead to TiO₂ accumulation in coral tissue.

What are the effects of titanium dioxide nanoparticles on plants and soil?

TiO₂, released into the environment through agricultural products, pigments or food additives, accumulates in soils where it comes into direct contact with plants. In the soil, nano-TiO₂ interacts with soil properties such as pH, microbial communities and enzymes, affecting its mobility and bioavailability. Studies show nano-TiO₂ can disrupt the diversity and activity of microorganisms essential to nutrient cycling, including those involved in nitrogen fixation and methane oxidation, by inhibiting their growth.

These particles can enter plant cells, affecting photosynthesis, metabolism, and gene expression. At high concentrations (> 2.0 mg/g soil), they reduce the activity of essential enzymes, which impairs plant growth and alters the composition of bacteria that support their development, compromising biodiversity and ecosystem function.

Toxicity and biocompatibility of titanium dioxide: A dual challenge for the environment.

The nano-TiO2 are common in various products but pose environmental risks. These particles do not break down easily and can persist in the environment for several years. Their small size allows rapid dispersion and increases the risk of toxic effects in aquatic ecosystems. Scientists are examining the impact of these nanoparticles on ecosystems and their accumulation in different species. Much remains unknown about their long-term effects on biodiversity. Further research is essential to understand these risks.

As a result, TiO₂ can have negative environmental effects when in nanometric form. It is essential to find solutions to improve its management. This requires clear rules to limit its use and measures to prevent its dispersal into the environment. Companies working with TiO₂ must also adhere to strict rules to ensure safety.