Biological effects of nanoplastics in paints

By Dr. Priyom Bose, Ph.D.Aug 24 2022Reviewed by Benedette Cuffari, M.Sc.

The high rate of plastic usage throughout the world and its subsequent uncontrolled deposition in landfills and water bodies have a significant effect on the environment. Although plastics are resistant to biodegradation, larger plastics are converted to smaller pieces when subjected to mechanical abrasion in hydrolytic surroundings or under ultraviolet (UV) irradiation.

When disintegrated plastics reach between one micrometer (µm) to five millimeters (mm) in size, they are referred to as microplastics (MPs). Microplastics further disintegrate to form nanoplastics (NPs), which are below 1,000 nanometers (nm) in size.

Study: Disentangling biological effects of primary nanoplastics from dispersion paints’ additional compounds. Image Credit: RHJPhotos / Shutterstock.com

Background

Primary NPs are synthesized for varied functions, such as additional ingredients in water-based dispersion paints and exfoliants in cosmetics. Although the use of NPs in cosmetics is declining, approximately 17 million tons of NPs are used in water-based dispersion paints every year for architectural coatings.

Oceans are also polluted through secondary MPs produced from paint abrasions from ship hulls. The environment is also polluted with secondary MPs from road markings and abrasions on the external surfaces of buildings.

A complex mixture of inorganic and polymer NPs and MPs is present in water-based dispersion paints. These compounds provide suitable paint viscosity, no drip property, and colloidal stability.

In most white paints, titanium dioxide (TiO₂) NPs are added and are released from painted facades during winter. Many model organisms, including the crustacean waterflea (Dapnia magna), have exhibited adverse effects following exposure to TiO₂ NPs. 

The toxic effect of TiO₂ NPs is enhanced due to synergistic effects with other compounds like cadmium and zinc ions, benzophenone, and parabens when absorbed by the organism.

NPs are absorbed by various organisms, primarily through adsorption on their surfaces and ingestion. This leads to bioaccumulation and biomagnification of NPs in numerous organisms.

Several in vivo and in vitro studies have revealed that NPs induce inflammation, produce reactive oxygen species (ROS), and are cytotoxic. Thus, it is imperative to determine the effect of compounds present in dispersion paints on organisms.

The effect of dissolved polymers in paints has not been evaluated, as their chain length indicates that they are non-toxic.

About the study

A recent Ecotoxicology and Environmental Safety study analyzed paint composition and its biological properties, as paints release polymers and particles into the environment. Some of the common components of paints include inorganic and polymeric NPs, dissolved polymers, and metal oxide MPs.

The current study evaluated the effect of every paint fraction at the cellular level using murine fibroblasts like L929 cells, and D. magna, which is a common indicator of environmental toxicity. To determine the impact of paint fractions, both of the aforementioned organisms were subjected to different concentrations of paint fractions. Cellular metabolic functions and D. magna immobility were also assessed.

Two wall paints (paint 1 and paint 2) were selected as possible representatives of household applications. Paint 1 was used for painting walls, whereas paint 2, which had a reduced dripping property, was used for painting ceilings. These paints were selected based on their components, which included TiO₂, silicon dioxide, calcium carbonate (CaCO₃), and polyacrylates, all of which are commonly present in most paints.

Study findings

Zeta potential indicated colloidal stability and its possible interaction with the biological system. The components of paint 1 showed a negative zeta potential for all tested pH values.

Furthermore, colloidal instability was observed at pH 3 with -5 mV zeta potential. Enhancement of the salt concentration also increased colloidal instability.

NPs with an average diameter of 98 nm exhibited colloidal stability. The zeta potential of paint 2 was comparable to that of paint 1. 

Toxicity levels associated with paint fractions were determined using the D. magna model. This experiment, using both paints independently, revealed that the median effective concentration (EC₅₀) of paints could immobilize 50% of D. magna when continually exposed for 48 hours. 

Further, the adverse effect of polyacrylates on organisms was reported. The dissolved copolymer of paint 2 was accumulated in the daphnid gut, which could lead to gut blockage.

This finding strongly indicates the possible toxic exposure of marine organisms to dissolved polymers.

Additionally, components of paint 1 were adsorbed onto the D. magna carapace.

An MTT cell proliferation assay using murine fibroblast revealed the metabolic activity of cells exposed to paint fragments, thus demonstrating their vitality. Conversely, L929 cell viability was strongly affected by nanosized components of paints with moderate zeta potentials.

Conclusions

The in vivo experiment revealed that dissolved polymers significantly affected D. magna. CaCO₃ and TiO₂ NP exposure led to decreased cell vitality.

A significant reduction in the metabolic activity of L929 cells exposed to metal oxides and plastic NPs was also observed.

Taken together, dispersion paints can induce varied biological responses in organisms and cells. In the future, innovative paint formulations should be developed to reduce their adverse effects on the environment.