How does paint pollution impact the environment?

Introduction

Probably seeing the beautiful, freshly painted facade of the house does not lead the observer to make an association with its possible impact on the environment. However, taking a broader picture it is quite clear that at least over the course of the last 50 years paint products are made of a variety of chemicals and synthetic pigments. Consequently, these chemical substances from the paint products used outdoors in one way or another find their way into the environment impacting different ecosystems and their inhabitants, including humans. This blog post focuses on the paint pollution impacts on the environment and ecosystems, providing information on how chemicals escape from painted outdoor surfaces and negatively impact air, soil, water and biota. To better understand how paint pollution impacts the environment, the following aspects will be explored:

• What is paint pollution and why does it matter;
• How does paint pollution happen;
• Which paint ingredients act as environmental pollutants and what damage they cause.

What is paint pollution and why does it matter?

There are three major types of environmental pollution: air pollution, water pollution, and land pollution. Paint pollution is generally defined by the introduction of harmful paint ingredients into the environment. Pollutants can be solids, liquids or gasses that are produced in higher concentrations than normal, thus reducing the quality of air, water or soil.  It is important to understand that Earth's atmosphere (air), hydrosphere (water), lithosphere (rock and soil) and biota (plants and animals) are interconnected, meaning that by causing harm to one of these components it leads to potential harm to others. Because all living things from microbes to humans depend on the Earth's resources, it is easy to understand that when the very basic ones like air and water are polluted, their well-being is subsequently threatened potentially causing cascading negative effects (a; b). 

Pollution of air 

Air pollution is defined by the presence of pollutants in air in large quantities for long periods of time. Typical air pollutants include CO, CO2, NO, NO2, SO3, dispersed particles, hydrocarbons and others. Air pollutants released by paint products contribute to formation of ground level ozone, known as smog and can also negatively impact the soil and water quality (b).

Pollution of water

Water pollution is defined by exceeded amounts of toxic chemicals and biological agents present in groundwater or other water bodies, as a result of human activities. Large bodies of water, for example the world's oceans act as a sink to chemical pollution either through pollutants accumulating in the aquatic sediments or accumulating in the aquatic organisms (c). 

Pollution of soils

Release of chemicals, such as hydrocarbons, pesticides or heavy metals leads to soil pollution. Because soil accumulates pollutants, it can act as a natural pollution sink leading to high levels of contaminants present, depending on soil type, degradability of pollutant and other conditions, that ultimately leads to pollution of the vegetation such as fruits and vegetables (d).   

How does paint pollution happen?

Pain pollution generally happens through three main pathways - air, water and soil, and they can be defined as following:

• off-gassing, when gaseous compounds escape into air;
• runoff, when chemical compounds are washed into water streams;
• leaching, when compounds are bound to soil particles or groundwater.

Off-gassing

Off-gassing or out-gassing describes release of airborne particles or chemicals that are known as volatile organic compounds (VOCs) and paint products are a significant source of VOCs in our environment. Through the process of off-gassing, paint products release VOCs in air, and more specifically in the lowest level of earth's atmosphere known as troposphere,  contributing to the formation of ground level ozone (e). 

Runoff

Runoff refers to water that flows on the surface because of no immediate possibility to be absorbed in land. Although runoff is mostly naturally occurring (for example when mountain glaciers and snow melt creating rivers and streams), human activity greatly impacts the amount of polluted runoff that comes either from point sources (source occupying a small area with concentrated output) or nonpoint sources (many diffuse sources over larger area).

Regarding the general public and their contribution to environmental pollution, the importance of nonpoint source pollution should be taken into account. It happens in urban, suburban and rural areas, where use of certain chemicals potentially leads to polluted runoff carrying contaminants into local streams and soils, for example, when paint products are washed away from buildings during rainfall or when the painting equipment is washed (f).

Leaching 

Leaching describes the process, when contaminants carried by water move downwards through permeable soils. Leaching is generally associated with the pesticide use in agriculture but it does in fact refer to numerous contaminants including other biocidal products and heavy metals that are both present in most traditional paints. Leaching from paint products happens as water washes down a painted surface or as paint deteriorates, allowing chemicals to bind to runoff waters and find their way into soils, thus leading to soil and plant contamination and potential groundwater pollution (g; h).  

Paint ingredients as environmental pollutants

Several paint ingredients consist of chemical compounds that sooner or later become environmental pollutants, mostly due to seemingly normal processes throughout paints’ life cycle. For example, drying on surface releases gaseous VOCs and washing off during rainfall releases biocides and heavy metals. Becoming aware of toxic ingredients present in paints it is possible to pay attention to their possible impact on the environment and subsequently also humans.  This blog post introduces to the VOCs, biocides and heavy metals that are present in architectural paints, and their impact on different ecosystems. 

Volatile Organic Compounds (VOCs)

Volatile Organic Compounds are fumes released from paint, among other products, during the product application and drying stages. VOCs are released from multiple paint ingredients, including solvents, co-solvents, coalescent agents, monomers and other possible volatile additives including biocides. Read more about VOCs in our blogpost: link

VOCs are paint ingredients, which are best known for their impact on human health, but these compounds also have a significant role as environmental pollutants. Namely, due to participation in formation of ground level ozone that further negatively impacts human health and causes damage to agricultural and natural vegetation.  

VOCs and ground level ozone

When VOCs are released in the atmosphere, they can react with sunlight and nitrogen oxides and form what is known as ground level ozone (also known as tropospheric ozone or smog). While naturally occurring ozone in the upper layer of Earth's atmosphere serves to protect all life on earth from the Sun's ultraviolet rays, ground level ozone is a result of human atrophogenic activities. Recognised by IPCC as one of the most important greenhouse gases, ground-level ozone (O3) is an atmospheric pollutant that negatively impacts environment and human health. Ground level ozone is known as a powerful oxidant and is one of the most widespread toxic agents vegetation is exposed to.  Elevated levels of ground-level ozone is the most damaging air pollutant to crops and ecosystems as it negatively impacts the agricultural yields of some plant species due to ozone interfering with photosynthesis process. 

Ozone affects vegetation entering their leaf openings known as stomata, that are responsible for plant respiration, causing oxidation or burning of the tissue, thus damaging plant leaves and threatening their survival. When ozone uptake reaches excessive levels, plants physiology is altered and reduced growth, reduced seed production, altered phenology and increased sensitivity to biotic and abiotic stresses can be observed. Prolonged ozone exposure can cause changes in plant gene expression and species composition. These impacts of ground level ozone thus potentially contribute to disruption in the main services provided by terrestrial ecosystems including disrupted food production, forest product production, water regulation, carbon sequestration and biodiversity conservation as a whole (i; j). 

Biocides

Biocides are defined by the European legislation (98/8/EC) as microorganisms or chemical substances meant to destroy, render harmless, deter or control a harmful organism through either biological or chemical means. Due to these characteristics biocides and biocidal products are added to conventional paint products to prevent biological growth on the paint during the in-can as well as dry film stage, meaning that architectural paints intended for exterior works are a significant cause of biocide pollution. Read more about biocides in our blogpost: link

Biocide polluted run-off begins at the painted surface where weathering takes place. At this point chemical compounds may become bound to the water cycle through the adsorption process and then potentially contaminating nearby surface waters, soils, ground waters and biota. Namely, biocides can further act in the environment in accordance with their manufactured purpose - which is by definition to limit or control biological activity (k; l). 

It is worth mentioning that most architectural paints will consist of combinations of different biocides, including herbicides, bacteriocides, algaecides, fungicides and metallions. Commonly used biocides in coatings include terbutryn, diuron, octylisothiazolinone (OIT) and others. Due to various material combinations in paint products it is generally difficult to control the amount or biocides that end up in the environment. Studies show that in urban environments common biocides can be detected in stormwater, surface water, waste water, groundwater and soil (m; n).

Overview of the applied biocides for building protection to prevent microbial growth (left) and the factors controlling microbial growth (right). Most important factors are indicated in bold (n).

Studies focusing on biocide pollution show that the amount of biocides released in the environment from building materials is significant in addition to that released by agricultural pesticides, but their nature is somewhat different. This can be explained by the fact that agricultural use of biocides is generally strongly regulated and involves specific location and time, while the biocide leaching from architectural paints, although in small amounts, is continuous over long periods of time and comes from many dispersed sources. Studies show evidence that biocides from paint products persist and accumulate in the environment and more specifically in surface waters and soils (n).

Biocides as water pollutants

Biocide polluted runoff water from urban dwellings is recognised as an increasing concern for aquatic environments, noting that known biocide concentrations in surface water and groundwater have been close to the regulatory threshold levels, where they can have biological effects (o).

Biodiversity of freshwater ecosystems is essential in providing numerous ecosystem services including drinking water, food and flood prevention indicating that the wellbeing of these systems is directly linked with the wellbeing of human societies. 

Biocide and biocide by-product pollution is known to be potentially highly toxic and harmful for aquatic ecosystems including aquatic plants, copepods and algae. Even in low pollutant concentrations biocide accumulation can take place in non-target organisms, leading to the risk of primary poisoning: as biocidal substance accumulates along the food chain even more organisms are at risk to secondary poisoning (q).

Biocides as soil pollutants

Biocide residues become soil pollutants through the process of leaching. As paint withers away and biocides become active substances in surface waters, this polluted runoff has potential to reach permeable soils, where biocide residues will move vertically down the soil profile. Because the mobility of organic compounds through soil is dependent on sorption processes, multiple physical and chemical factors of both the given soil and the pollutant will determine the mobility of active biocidal residues (h).

  Soil fertility is largely dependent upon the biological activity of many different soil organisms, therefore soil pollution with life-controlling biocidal substances has direct negative impact on the soil microbiome. While it is hard to determine biocide activity in soils, since it varies greatly depending on multiple factors, it's argued that even at very low concentrations biocides may cause significant changes in soil biological and chemical properties and soil microorganisms.

Additional problem regarding biocide pollution in soils concerns pollutants leaching deeper through the soil profile and penetrating groundwater level. In the groundwater water-soluble biocides are no longer continually diluted as it is in the surface water, namely, very little or none of the biocides are broken down increasing their hazardous potential (p). 

Biocide pollution impact on plants and animals

Biocides are products designed to kill or control target organisms, but it is known that in addition they have a potential to kill or control nontarget organisms. For example, if biocides above certain threshold concentrations find their way into water, they can have an ecotoxic effect on algae, aquatic plants and animals. Biocides have the ability to interfere with DNA synthesis and photosynthesis, which are essential for plant survival.  Biocides pose long-term risks to mammals, birds, amphibians and fish as a result of biocide accumulation in the food chain. As bodies of water can become pollutant sinks, it is not unlikely that smaller aquatic organisms will absorb water pollutants directly, and further as they are eaten by larger animals the pollutant can accumulate in significant and life-threatening concentrations. This phenomenon is called biomagnification, where organisms (including humans) higher on the food chain have larger concentrations of pollutants in their bodies than the smaller ones. Thus, biocide pollution can be harmful not only to natural ecosystems, but also to human health (r; s; q).

Heavy metals

One of the compounds in traditional paints are inorganic coloured pigments that are known for containing heavy metals including titanium dioxide, iron oxides, aluminum and mica flakes. Other heavy metals present in paint may include cadmium, mercury and lead.  Heavy metals are common environmental pollutants and their concentrations in air, water and soil keep increasing due to human activities. This is a very specific type of pollution, because heavy metals are not biodegradable and tend to accumulate in organisms and cause numerous diseases and disorders (t; u).

Heavy metals as water and soil pollutants 

Heavy metal polluted runoff from multiple diffuse spots carries the substances towards bodies of water, where they become consumed by aquatic fauna leading to further pollutant uptake by species higher in the food chain, including humans.  Heavy metal pollution is considered one of the major types of soil pollution, where copper, nickel, cadmium, zinc, chrome and lead are considered main pollutants. Through the process of leaching, contaminants carried by the runoff waters travel vertically down soil profile. Studies indicate that even low concentrations of the heavy metals affect plant physiological metabolism, but as small amounts accumulate, the negative effects become even greater impacting different parameters of soil microbial communities and parameters that influence plant quality and yield.  Considering heavy metal accumulation, it is known that heavy metals that are deposited in soils are transported to vegetation and further to the food of animals and humans. It could potentially lead to multiple health problems linked to heavy metal poisoning including internal organ damage, tumour development and fetal development issues. It is worth mentioning that heavy metal accumulation in the body is irreversible (v). 

Closing

Uncontrolled chemical pollution imposed by human anthropogenic activities is known to have a negative impact on ecosystems, including air, water, soil and biota. Paint ingredients, such as volatile organic compounds, biocides and heavy metals, impact the environment by interfering with the chemical balance of sensitive natural systems. It is well known that gaseous compounds from paint products contribute to the formation of smog and it is also well known that heavy metals and substances intended for controlling organic life are accumulating in living systems that include waters and soils as well as animal and human bodies. Recognising potential harm from certain paint product ingredients - not only to the nature, but also to the human health – could motivate the consumers to choose: A) more environmentally friendly products; B) products that have a list of ingredients available; or C) products having a label indicating low or safe amounts of harmful ingredients.   

Author: written by Anse Romančuka, edited by Linda Kikuste