Water pollution is one of the leading environmental and social issues in the world.
Water pollution includes pollution of both fresh water sources (lakes, rivers and groundwater aquifers), and also ocean/marine water pollution.
In this guide, we’ve outlined what water pollution is, the different types of water pollution, along with causes, sources, examples, effects & potential solutions.
Summary – Water Pollution
- Water pollution is a major environmental and social issue
- It involves the pollution or contamination of a body of water, that leads to a degradation of that body of water, and can result in negative effects on human health, wild life and living organisms, the environment and it’s ecosystems, and the economy
- There are many different types of water pollutants and contaminants that come from both man made and natural sources
- Water pollutants are often found in different types of waste such as wastewater or sewage, just to name two examples
- Man made pollutants come from all areas of society – households, industry and agriculture
- There are many different ways that pollutants and contaminants can get from their origin source into a clean water source
- Pollutants may degrade the water directly, or there may be some type of secondary reaction first before water pollution and degradation happens
- Two of the major causes for water pollution in the world are agricultural pollution in the form of nutrient pollution, and waste water and sewage pollution resulting from untreated sewage and waste water. But, there are others such as industrial waste pollution (especially in the ocean)
- There are different types of water sources that get polluted – surface water sources (lakes, rivers, etc), ground water sources, and marine/ocean water
- These water sources are polluted via a single point, dispersed/multiple points, or, from an original point in another region or country
- Different countries and cities across the world face different levels of water pollution – India and China are two notable major countries with significant levels of water pollution. What is interesting though is that even developed and considerably wealthy nations are experiencing levels of water pollution in surface and ground water sources, and also water contamination in drinking water and tap water (the US it one example)
- Likewise, some countries are responsible for more water pollution than others. Some lists show China, the US, India, Japan, Germany, Indonesia and Brazil among the top polluting regions
- Solutions to water pollution will ultimately be custom solutions to a specific geographic location or city, because each location has different causes of water pollution, and different capabilities to address water pollution (developing and low income regions are likely more vulnerable to and less capable to address water pollution issues than developed and higher income regions)
- Solutions may focus around reducing the main sources of water pollution, and cleaning up and treating (to make them safe and clean according to the relevant water quality test or standard) the water sources that are already polluted
- Water pollution is incredibly important to address now and in the future not only because of the effects it is already having, but also because water demand and populations are projected to grow, whilst usable water supplies are projected to decrease (demand is outpacing supply … leading to limited water availability)
- Although water augmentation (such as desalination) technology exists to create more fresh water, it’s still important to address and manage water pollution
What Is Water Pollution?
- Water pollution happens when harmful substances, pollutants or contaminants (such as chemicals or microorganisms) contaminate a body of water, degrading water quality, and resulting in some type of negative impact for humans, animals and living organisms, the environment, or some other aspect of society such as the economy
Main Types Of Water Pollutants
Waste pollution and water pollution are closely linked, as waste material itself can water, but waste can also carry certain types of pollutants and contaminants.
Pollutants and the waste that carries them, can come in many forms – liquid, solid, gas, micro organisms – just to name a few.
Some of the main types of pollutants and pollutant carrying wastes are:
- Waste water (used water) and storm water run off (from sinks, showers, and toilets, and from commercial, industrial, and agricultural activities)
- Sewage and septic system waste
- Leachate from landfills
- Industrial chemicals
- Heavy metals and solvents, and toxic sludge
- Household chemicals, waste and products (for example, cleaning products, as well as personal care products and pharmaceuticals, such as birth control pills, painkillers and antibiotics)
- Organic chemicals (chemicals produced in a lab)
- Greenhouse gases (carbon emissions are absorbed by the ocean)
- Air Pollutants
- Solid Debris like Plastic (can be inadequately disposed of, or littered)
- Oil, gasoline, break fluid, grease
- Heat (via thermal water pollution – such as discharge of heated water from a power plant)
- Radioactive substances
- Mine Tailings and effluent
- Pollution from bacteria and microorganisms like microbes, viruses, pathogens, parasites, and protozoa (high levels of pathogens are usually caused by a lack of proper sanitation systems, and/or untreated sewage getting into a water source)
- Natural pollution from volcano eruptions, earthquakes, flooding and tsunamis
- Anaerobic Organisms
- Suspended Particulate matter (and other sediments)
- Biodegradable waste like animal manure (especially from livestock) or urine, and naturally decaying plant material
- Other Types Of Waste Or Pollutants (medical, industrial, toxic, domestic, food wastes, carcinogens and so on)
- [Whilst not technically a pollutant or contaminant, some water may be brackish or semi saline water. Brackish water may have a salt content somewhere in between salt water and fresh water, and may happen when fresh water mixes with salt water, or in brackish fossil aquifers]
Some types of waste carry a common pollutant. For example, wastewater, fertilizers and sewage can all contain nutrients (nitrates and phosphates) – and nutrient pollution is a type of water pollution in itself.
Where Do Water Pollutants Come From?
Water pollutants can come from a range of both human and natural sources,
Some of the main places that water pollutants come from are:
- Industrial Sites
- Construction and Building Sites
- Households & Personal/Consumer Products
- Roads/Highways, Pavements & Impermeable Surfaces
- Commercial Buildings
- Nature (air, soil, other water sources, animals, micro organisms)
- Waste Management Sites (landfills)
- Sewage and Water Treatment Plants
- Water Infrastructure Like Pipes
- Storm Drains & Sewers
- Ships & Sea Vessels
- Below Ground Storage Tanks
- Metal Ore Mining Sites
- Uranium Mining, Nuclear Power Plants, and the Production and Testing of Military Weapons (in the case of radioactive waste)
Human based sources … are the main contributors to water pollution (nrdc.org).
Causes Of Water Pollution (How Water Pollution Happens)
There are many causes and different ways that water pollution can occur. Some of them are:
- Direct dumping or discharging of treated or untreated pollutants or waste into a water source
- Loss or spill of pollutants or waste directly into a water source
- Run off of pollutants from a soil, pavement or road surface (or some other type of surface)
- Leaching, percolating or seepage of pollutants from soil into water, or from other polluted water sources into a new water source
- Absorption of pollutants from the air
- Littered or inadequately disposed of waste or pollutants being washed or blown into a water source directly, or into a system that leads to the water source, by the wind/air, rain or ocean tide
- Pollutant/s or contaminants develop naturally in the water source
- [An indirect way water pollution can occur is also water politics or poor political management of water quality that leads to conflicts of interest, and poor management and pollution of water sources]
Specific examples of the above are:
- Untreated sewage or waste water being discharged directly into water sources, or industrial sludge and dredging being dumped directly into the ocean by businesses and industrial organisation.
- Fishing gear being lost or dumped into the ocean from a fishing vessel. Another example is oil being spilt or lost into a water source from an oil tanker or an oil rig
- Pollutants in contaminated soil being washed by rain through the crevices in the soil into ground water sources. For example, pesticides are sprayed onto crops, soak into the soil, and can be washed down into ground water sources
- Waste like plastic being washed into storm drains and sewers, and flowing out to the ocean
- Wind blowing solid debris like plastic, cigarette butts and paper bags into the ocean, and the tide washing beach litter into the ocean. The wind may also blow chemicals like pesticides into water sources (this is called pesticide ‘drift’)
- Water sources absorbing carbon or air pollutants from the air
- Acidic rain (from air pollution) mixing with water sources
- Nuclear waste that isn’t properly contained, managed or buried can contaminate water sources
- Discharged mine effluent and seepage from tailings and waste rock, and other waste
- Chemicals found in public water pipes can leach into the public water supply
- Rainwater harvesting from roofs with oil based lead paint can pollute water
- Contamination of soil by landfill leachate, and then leaching from the soil into a water source. Pesticides can also leach or percolate from soil into water sources (read more about the 4 major routes pesticide reaches and pollutes water in the Wiki guide listed in the sources list)
- Run off of chemicals from soil or road surfaces into water (e.g. runoff of pesticides from farms, or runoff of oil from roads)
- One polluted water source converging with or washing into another clean water source, and polluting that new clean water source (e.g. from a river, to a bay, to the ocean)
- Animals carrying waste or pollutants into water sources, or urinating, bathing and defecating in water sources
- People carrying waste or discharging of waste into water sources (via bathing, urinating and defecating)
- Other biodegradable waste like plant life may grow in and around water, leading to an imbalance or certain micro organisms. Also, too much biodegradable waste in the water can lead to more micro organism growth and increased oxygen being used in the water and eventually depleted … and, this leads to aerobic organisms dying, and anaerobic organisms growing. This could happen for example after a natural disaster or natural event like a flood or hurricane where biodegradable waste is upended and carried into water sources
- Viruses, pathogens, bacteria and protozoa, or other types of micro organisms (aerobic and anaerobic) developing naturally in the environment due to some type of natural process. A lack of clean/safe water treatment, hygiene and sanitation infrastructure, facilities, and technology can be part of this problem
Once in the water, some pollutants react in a certain way or settle in a certain way that causes a further loss in water quality. A few examples are:
- Nutrients – wastewater, fertilizers and sewage contain nutrients. Nutrients encourage algae and weed growth, and algae deplete the water of oxygen, along with weeds clogging up water which needs to be filtered or treated in some way (eschooltoday.com).
- Anaerobic Organisms – in water, they can produce harmful toxins such as ammonia and sulfides (eschooltoday.com).
- Suspended Particulate Matter – certain types of pollutants or even biodegradable material may not dissolve easily in water and wash away or dilute. If it doesn’t, it can either stay suspended on the surface of the water, or settle in sediments on the bottom of a water source (water-pollution.org.uk)
It’s also important to mention that some pollutants are a primary type of waste or pollutant that cause direct pollution. But, other pollutants come from a secondary source where primary pollutants react or interact with each other, or other compounds, and cause a more indirect form of water pollution. A few examples are:
- Ocean acidification – an ongoing decrease of the ocean’s pH level, from absorption of CO2 in the air
- Acid Rain – Acid rain has many ecological effects, especially on lakes, streams, wetlands, and other aquatic environments. Acid rain makes such waters more acidic, which results in more aluminum absorption from soil, which is carried into lakes and streams. That combination makes waters toxic to crayfish, clams, fish, and other aquatic animals (nationalgeographic.com)
Depletion of groundwater and droughts can cause salinity issues in water sources as well – although this isn’t traditionally seen as water pollution – it is a water quality issue.
Most Common Causes/Sources Of Water Pollution
In each country, and each region within a country, different water sources (ground water, surface water, or ocean water) may be polluted by different pollutants, and pollutants may come from different sources.
But, as a general guide …
The most significant sources of water pollution [globally] are:
- … lack of inadequate treatment of human wastes, and
- … inadequately managed and treated industrial and agricultural wastes
The most common causes and sources of water pollution globally are:
- Agricultural water pollution (nutrient pollution is the number one threat to water quality worldwide, and cause have a negative side effect of algal blooms)
- Sewage and waste water pollution – particularly from untreated sewage and waste water (waste water contains all types of chemicals, and sewage contains chemicals from the things humans consume, as well as viruses and pathogens)
- Oil pollution (oil and gasoline that drips from millions of cars and trucks every day, and from factories, farms, and cities)
- Radioactive substances
Read more about causes and sources of water pollution (nrdc.org)
For surface water specifically in the United States:
- Nutrient pollution, which includes nitrates and phosphates, is the leading type of contamination in … freshwater sources
- [nutrient pollution mainly comes from farm waste and fertilizer runoff … especially when it rains and nutrients run off into water ways]
- Municipal and industrial waste discharges contribute a fair share of toxins as well. There’s also [waste from] industry and individuals dumped directly into waterways
And, for ground water:
- … [it is] polluted when contaminants—from pesticides and fertilizers to waste leached from landfills and septic systems [get into aquifer sources]
- [ground water sources can be hard to clean, and can cross contaminate other water sources like lakes and rivers]
There is a graphic available about planetary boundaries (stockholmresilience.org)
This graphic illustrates how reactive nutrient supply levels of nitrogen and phosphate (from agricultural and industrial activities) in the biosphere (and water sources) are one of the planetary boundaries that have reached the point of high risk/beyond the zone of uncertainty.
More common/major causes of water pollution can be seen here (explainthatstuff.org)
They note that the US has invested heavily in improving waste water treatment plants. Although it is less clear what the trends are for improvement in nutrients and sewage water pollution are.
Causes Of Water Pollution Specifically In Developed Countries
The water pollution causes in developed countries can be different than developing countries.
Developed countries may face these causes as the most common for water pollution:
- Agriculture – is the biggest cause of local water pollution in developed countries [specifically, pesticides and other agricultural chemicals pollute groundwater and surface water, leading to high concentrations of nitrates, that can result in algal blooms]
- Factories & Industrial Pollutants – [toxic chemicals in waste water are dumped directly into freshwater sources, and it happens in almost every developed country]
- Transport & Vehicles – Fuel and oil run off from vehicles and roads into freshwater sources. Especially an issue in cities, and highly populated places with more people and more vehicles
- Air Pollution – air contaminant emissions from vehicles and power plants. Air pollution causes issues like acid rain that rains back down into freshwater water sources (as well as onto soil) and pollutes it
Causes Of Water Pollution Specifically In Developing Countries
Developing countries may face these causes as the most common for water pollution:
- Waste Management & Sewage Management – in small towns, villages and rural areas, there’s often no dedicated sewage or septic systems available. Because there is no contained way to dispose of human waste, ground water and surface water can be contaminated, and this leads to the spread of bacteria, illness, and parasites
- Agricultural – happens in a different way to developed countries. The agricultural systems and technology is often more primitive and simple (and not as advanced). Waste management is a problem here … since animal waste isn’t disposed of properly and dead animal bodies are usually not either
Causes Of Local Water Pollution In Specific Countries & Cities
You can read this guide for some of the causes of water pollution and contamination in some of the major water sources in China, the US, India, Japan, Germany, Indonesia and Brazil (all-about-water-filters.com)
You can read this guide for some of the causes of water pollution and contamination in the Ukraine and other countries (bestlifeonline.com)
You can read this guide for some of the causes of water pollution and contamination in places across Africa, Central & South America, the US, and Asia and The Middle East (all-about-water-filters.com)
Types Of Water Sources That Get Polluted
There’s three main types of water sources that can get polluted:
- Surface Water Pollution – pollution of above ground water sources like rivers and lakes
- Ground Water Pollution – pollution of underground water aquifers (these aquifers are formed when water from rain and rivers seeps into the ground and accumulates within cracks or pores in the rocks)
- Ocean Water Pollution – pollution of the sea/marine environment
Surface and ground water pollution are mainly fresh water pollution issues.
Ocean water pollution is really an issue on it’s own, separate to fresh water or land based water pollution.
- Nearly 40 percent of Americans rely on groundwater, pumped to the earth’s surface, for drinking water.
- For some … rural areas, it’s their only freshwater source.
- Groundwater gets polluted when contaminants—from pesticides and fertilizers, to waste leached from landfills and septic systems—make their way into an aquifer
- [Polluted ground water can contaminate other sources of water and seep into streams, lakes, and oceans]
Read more about groundwater pollution in these guides:
Surface Water Pollution
- Surface water … accounts for more than 60 percent of the water delivered to American homes
- According to the most recent surveys on national water quality from the U.S. Environmental Protection Agency, nearly half of … rivers and streams and more than one-third of … lakes are polluted and unfit for swimming, fishing, and drinking
- Nutrient pollution, which includes nitrates and phosphates, is the leading type of contamination in … freshwater sources
- [Nutrient pollution mainly comes from farm waste and fertilizer runoff].
- Municipal and industrial waste discharges contribute a fair share of toxins as well. There’s also [waste from] industry and individuals dumped directly into waterways
Read more about surface water pollution in this guide (pollutionissues.com)
Ocean Water Pollution
- Eighty percent of ocean pollution (also called marine pollution) originates on land—whether along the coast or far inland.
- Contaminants such as chemicals, nutrients, and heavy metals are carried from farms, factories, and cities by streams and rivers into … bays and estuaries; from there they travel out to sea
- [Plastic is commonly found in the ocean]
- [Oil from vehicles, households and industry’
- [The ocean also absorbs as much as one quarter of man made carbon emissions from the atmosphere]
Read more about marine pollution in this guide (nrdc.org)
Number Of Points At Which Water Pollution Can Occur, & Boundaries Of Water Pollution
Water isn’t always polluted at one single point. It can can polluted or contaminated from multiple points.
Water pollution can also come from outside of the country or region where the pollution takes place.
How water pollution can occur can include:
- Point Source (pollution from a single point/source)
An example might be a single discharge pipe for waste water/effluent
- Non Point Source (pollution from multiple points/sources)
An example might be pesticide which can drift in the air and pollute water, and, sink into soil and pollute ground water from multiple points. Another example can be one body of water being polluted from several different points with several different types of pollutants – we see this in the ocean when all different types of industrial waste can be dumped into it
Nonpoint source pollution is the leading cause of water pollution in U.S. waters, but it’s difficult to regulate, since there’s no single, identifiable culprit (nrdc.org)
- Transboundary (pollution that originates from over another country or region)
For example, pollution in a river in one country may cause fresh water or ocean pollution in another country if that river spans or connects into a water source in another country. Similarly, an oil spill in the ocean of one country may drift to the ocean of another.
Effects/Impact Of Water Pollution
Each different water pollutant and/or contaminant can have a different set of effects.
But, the main effects of water pollution include:
- Impact On Human Health – humans use, drink and bathe in water (amongst other uses). Polluted water can cause health issues/diseases, and contribute to premature death.
- Impact On Wild Life & Animals – Animals live in, drink and bathe in water. Water pollution degrades the aquatic environment they live in, and can cause health issues/diseases, and contribute to premature death.
- Impact On The Natural Environment – Plant life and soil for example can depend on water in one way or another. Polluted water can degrade the natural environment and degrade ecosystems in several ways.
- Impact On The Economy – Water is not only used in many of our daily activities, but for business for many of the products and services we offer and use. In addition to that, there is the economic cost to clean up and treat polluted water.
The effects of water pollution are usually experienced when:
- There is direct consumption of the polluted water (drinking, or inhaling/ingesting it)
- There is exposure to the polluted water (such as an aquatic species that lives in the water, or there is direct or close contact with that polluted water source)
- The water needs to be used for a certain purpose (business, cleaning/bathing, agriculture and food production, recreation, fishing etc.)
Read more about the effects of water pollution in this guide (nrdc.org)
Impact Of Water Pollution On Humans & Human Health
Some stats to consider:
- … low-income communities are disproportionately at risk [to water pollution] because their homes are often closest to the most polluting industries
- [Water pollution] caused 1.8 million deaths in 2015
- Every year, unsafe water sickens about 1 billion people
- Every year 3,575,000 people die from water related diseases
- Globally, 1.5 million children under five die and 200 million days of work are lost each year as a result of water-related diseases
Impact Of Water Pollution On Animals & Wild Life
Just some of the effects on wild life and animals can include:
- Eutrophication can create ‘dead zones’ in the water where there is a lack of oxygen for aquatic species living in them
- Pathogens and bacteria in water can make animals sick
- Algal blooms can produce neurotoxins that affect wildlife, from whales to sea turtles (nrdc.org)
- Chemicals and heavy metals can be toxic to wild life, and predator species can accumulate toxins like mercury from eating prey species
- Plastic and other solid debris can be ingested by wild life or they can become entangled in plastic nets and other solid waste material
- Ocean acidification (when water becomes more acidic) impacts marine species like shellfish and coral
Impact Of Water On The Environment
- [Water pollution generally disrupts the] complex web of animals, plants, bacteria, and fungi … which interact, directly or indirectly, with each other
- … this leads to a chain effect in the environment where plant life and living organisms can be affected, but also the soil, air and other water sources
Impact Of Water Pollution On The Economy
The overall impact of water pollution on the economy is hard to estimate because of the different sources of water pollution and the various industries they each impact.
But, nutrient pollution alone in the US has costs to remove nitrates and algal blooms from drinking water (can cost in the billions to clean up one water source), there are tourism losses (close to $1 billion a year), commercial fishing and shellfish losses (can be tens of millions of dollars a year), and real estate losses.
Read more about nutrient pollution in this guide (epa.gov)
- [In some region in the world, such as India, water pollution can reduce GDP growth by a third or a half]
- [Water pollution can also reduce agricultural revenues, as well as agricultural yields]
- The health costs relating to water pollution [in India] are alone estimated at about INR 470-610 billion ($6.7-8.7 billion per year) – most associated with diarrheal mortality and morbidity of children under five and other population morbidities
Potential Solutions To Water Pollution
One example of a good solution could lie within water recycling via waste water treatment and reuse.
As a summary, there are general solutions to water pollution such as reducing or eliminating water pollutants and waste before they pollute a water source, and also treating and cleaning water that has already been polluted.
But, each local body of water that has been polluted also needs it’s own custom water pollution solution strategy with solutions being implemented.
Some of the key things to be aware of are:
- Identify the water source that is being polluted or contaminated (usually a surface water, ground water, or marine water source)
- Identify the main pollutants and contaminants (e.g. industrial chemicals and waste water)
- Identify the source they are coming from (e.g. factories in the area)
- Identify the point/s at which they are polluting or contaminating the area (single point, or multiple/dispersed points?)
- Identify the IMPACT of the water pollution – how significant is the impact it’s having on humans, wild life, the environment and the economy?
- Identify how you are going to reduce or eliminate pollutants and waste getting to the identified point/s from the identified sources – does it involve waste and pollutant treatment and management systems? Are new or better enforced waste and pollutant laws and regulations required? Etc.
- Identify how you are going to remove waste and pollutants from the water, and make it clean and safe again
- [It’s possible that other water sources are being cross contaminated by the first water source, and these water sources would need to be assessed too]
But, there’s also major challenges and problems associated with addressing and solving water pollution and contamination issues, which is why water pollution and contamination issues still exist.
How To Measure Water Quality
Some countries have different water quality guidelines and standards for different water uses.
For example, the standards and testing in place for drinking water are usually different to the testing that takes place for water used for irrigation and industry.
Water’s physical and characteristics are usually tested against these guidelines to get an assessment of water quality.
In the case of drinking water, water may be tested and monitored continually to make sure it meets certain standards to be clean and safe for drinking.
But, water can be tested for different end uses, and also for concentrations of specific minerals, chemicals, pollutants and contaminants.
Most Common Water Quality Problems
- Globally, the most prevalent water quality problem is eutrophication, a result of high-nutrient loads (mainly phosphorus and nitrogen), which substantially impairs beneficial uses of water.
- Major nutrient sources include agricultural runoff, domestic sewage (also a source of microbial pollution), industrial effluents and atmospheric inputs from fossil fuel burning and bush fires.
- Lakes and reservoirs are particularly susceptible to the negative impacts of eutrophication …
- Nitrogen concentrations exceeding 5 milligrams per litre of water often indicate pollution from human and animal waste or fertilizer runoff from agricultural areas.
Another notable water quality problem might be:
- An emerging water quality concern is the impact of personal care products and pharmaceuticals, such as birth control pills, painkillers and antibiotics, on aquatic ecosystems.
- Little is known about their long-term human or ecosystem impacts, although some are believed to mimic natural hormones in humans and other species.
There is a table available in this guide (wikipedia.org). This table identifies the food type with the highest levels of eutrophying emissions per 100 grams of protein. Beef, farmed fish, farmed crustaceans, cheese, lamb and mutton, pork, and poultry (in that order from highest emissions to lowest), are some of the foods with the highest emission levels.
Why Is Water Pollution & Degradation Of Water Quality A Problem?
Apart from the effects listed above in this guide, water pollution is a problem because:
- Because we use water for almost everything we do in society – drinking, bathing, industry and business, food production and agriculture, and so on. There is a water footprint for essentially all everyday products we buy and the foods we eat
- Poor water quality decreases or completely eliminates the amount of available useable (safe and clean) water in an area. This is a potential issue when you consider projections for 2050 estimate that billions of people globally will be living with limited access to water, and in many cities around the world, demand will be outpacing supply. By 2050, global demand for freshwater is expected to be one-third greater than it is now (nrdc.org)
Water Pollution vs Water Contamination: What’s The Difference?
What is important to note is that a developed country like the US may mostly have access to safe drinking water (by some standards), but harmful contaminants can still be found in tap water in different States in the US.
Some of the most common contaminants found in US tap water are lead, atrazine, pathogens, chlorine treatment by-products, arsenic, nitrates, radioactive contaminants, vinyl chloride, perchlorate, and pharmaceuticals (nrdc.org)
Which Countries Have The Worst Water Pollution?
Which Countries Are The Biggest Water Polluters?
Some Water Pollution Stats
- Globally, 80% of wastewater flows back into the ecosystem without being treated or reused
- Read more about waste pollution stats in this guide
- Every day, 2 million tons of sewage and other effluents drain into the world’s waters.
- Every year, more people die from unsafe water than from all forms of violence, including war
- In the United States, pesticides were found to pollute every stream and over 90% of wells sampled in a study by the US Geological Survey
- Pesticide residues have also been found in rain and groundwater