Why is there lead in older neighbourhoods and urban soils?

Why do we find nasty organic chemicals and heavy metals in old orchards?  What are the contaminants  left behind by factories, landfills, dry cleaners, gas stations,  and other industrial and commercial land uses? What contaminants are released in an oil spill? What happens when these toxic legacies get into our environment, our soils, our water, our food, and our bodies?

When it comes to earth repair and grassroots bioremediation, knowing what sort of contamination you are working with allows you to engage in the appropriate clean-up techniques, as well as properly protect yourself and the folks in your community.

Also, when looking to clean-up a site, we have to ask ourselves whether we are dealing with metals, chemicals, or both. If you are dealing with heavy metals, remember that they can be bound and extracted, but not broken down. When dealing with chemicals, remember that unlike metals, they can be broken down.

Below is a list of some of the common contaminants you may find on your site. There are many contaminants not listed here that may be present in the environments you are working with, but this is a good place to start.

Heavy Metals

Arsenic (As)

Mining, smelting of nonferrous metals and the burning of fossil fuels are the major industrial processes that lead to arsenic contamination. Arsenic is also used in pesticides, herbicides, insecticides and as a preservative in pressure-treated lumber and wood products. In agricul- ture, organic arsenic compounds have been used in many agricultural insecticides and poisons, mainly on orchards and cotton fields. These compounds have also been used in livestock production as a controversial additive in animal food which supposedly stimulates growth and prevents disease. Other industrial products containing arsenic include lead-acid batteries, lead shots and bullets, some forms of glass, light-emitting diodes, paints, dyes, pyrotechnics, metals, pharmaceuticals, soaps and semiconductors.

Arsenic poisoning and long term exposure can lead to cancer of the skin, lung, bladder, kidney, liver and prostate. Breathing high levels of inorganic arsenic can give you a sore throat or irritated lungs, and ingesting very high levels of arsenic can result in death. Exposure to lower levels in the short term can cause nausea and vomiting, swelling and redness of the skin, decreased production of red and white blood cells, abnormal heart rhythm, damage to blood vessels and a sensation of “pins and needles” in hands and feet .

Cadmium (Cd)

Humans put cadmium into the environment by burning fossil fuels, coal and municipal solid waste, using phosphate fertilizers and producing iron and steel, cement and nonferrous metals. Cadmium is a minor component in most zinc ores and therefore is a byproduct of zinc production. It is also found products such as batteries, paints and pigments, metal coatings and plastics. Cadmium can travel long distances before depositing in water or soil, and it binds strongly to soil particles.

Breathing high levels of cadmium can severely damage the lungs, and ingesting food or water with very high levels severely irritates the stomach, leading to vomiting and diarrhea. Long-term exposure to lower levels leads to a buildup of cadmium in the kidneys and possible kidney diseases, as well as lung damage and fragile bones.

Lead (Pb)

Lead is currently used in building construction, lead-acid batteries, fusible alloys, pewters, bullets and shots, weights, as part of solders and as a radiation shield. In the construction industry, lead sheets are used as architectural metal in roofing material, cladding, flashing, gutters and gutter joints and on roof parapets. Lead is also frequently used in PVC (polyvinyl chloride) plastic, which coats electrical cords, as well as a coloring agent in some ceramic glazes. Some lead compounds are used as an additive for aviation fuel in piston-driven aircraft, and lead-based semiconductors are being used in photovoltaic cells (solar energy) and infrared detectors. Lead mining and smelting are also sources of environmental contamination globally.

Many older houses and buildings used lead-based paint, and as the paint ages, it chips off and mixes with the soil, which is why lead levels in residential soils tend to be highest closest to buildings. Lead was a component of the paint used on children’s toys — now restricted in many countries. Prior to 1978, most fuels contained lead, and the exhaust from cars would deposit lead oxide onto soils near heavily trafficked roads. Most countries stopped using leaded gasoline as of 2007. Lead contamination may also come from leaded gasoline leaking from old underground storage tanks (at gas stations for example). Until the early 1970s, lead was also used for joining cast-iron water pipes and used as a material for small diameter water pipes. Any place where an older structure has burnt down will likely have lead contamination. Finally lead was used in pesticides before the 1950s, mainly for fruit orchards.

Lead damages the nervous system, especially in young children, as it is a neurotoxin that accumulates in both soft tissues and bones. Lead has been proven to permanently reduce the cognitive capacity of children at extremely low levels of exposure, causing learning and behavior disorders. It causes blood and brain disorders and is toxic to the heart, bones, intestines, kidney and reproductive systems in both adults and children. Exposure can lead to small increases in blood pressure and can cause anemia. Exposure to high levels of lead can cause brain and kidney damage, as well as lead to miscarriages in pregnant women. Chronic, high-level exposures of lead have been found to reduce fertility in men. High levels of lead in the blood are associated with delayed puberty in girls.

Chromium (Cr)

Natural sources of chromium compounds are present in the environment from the erosion of chromium-containing rocks and can be distributed by volcanic eruptions. The mined metal form of chromium is used for making steel, for chrome plating, dyes and pigments, leather tanning, brick making and wood preserving. Chromium is found in cement. Elevated levels of chromium can also be found in the air and soil near busy roads due to emissions from car brake lining and catalytic converters containing chromium. As a result of its widespread use, chromium compounds are often found in soil and groundwater at abandoned industrial sites. Primer paint containing chromium compounds are still widely used in aerospace and automobile refinishing businesses.

Health impacts from exposure to chromium include irritation to nose and skin, itching, nosebleed, sneezing, liver damage and cancer. Chromium is a known carcinogen.

Mercury (Hg)

Mercury is used primarily for the manufacture of industrial chemicals or in electrical and electronic applications. Mercury contamination can occur through the production and the improper disposal (e.g. landfilling, incineration) of the waste stream of products that contain mercury such as batteries, fluorescent light bulbs, paint, thermometers, barometers, medical products, electrical switches, float valves, explosives, gold recovery, electrochemistry and tooth fillings. Coal plants are another major source of mercury contamination. Gold mining and production also accounts for mercury emissions and contamination, as well as nonferrous metal production and smelting. Oddly enough, mercury, as thimerosal, is widely used in the manufacture of mascara. Liquid mercury has been used as a coolant in some nuclear reactors, and before 1995 mercury was present in some herbicides and wood preservatives. It is also used in the production of chlorine and caustic soda at chlor-alkali process plants. Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines, and water runoff from such sites is a recognized source of ecological damage. These mines and processing plants can be extremely toxic and contaminated places.

When mercury collects in rivers, lakes and streams and combines with rotting plants in oxygen-deficient conditions, it can turn into the more toxic methyl mercury. Even a very small amount of methyl mercury can poison all the fish in a pond or river. Methyl mercury in the environment is toxic for centuries. Conditions in the reservoirs of big dams can lead to formation of methyl mercury.

Mercury can cause skin rashes and impact the lungs and eyes. Methyl mercury is a potent neurotoxin capable of impacting neurological development in fetuses and young children and damaging the central nervous system of adults. Symptoms include impaired balance, numbness in hands and feet, muscle weakness, damage to hearing and speech and narrowing of the field of vision. In extreme cases, insanity, paralysis, coma and death can occur within weeks of the onset of symptoms. Exposure to mercury is most likely to occur at harmful quantities through consumption of fish contaminated with methyl mercury, as well as other food sources where mercury has bioaccumulated. Exposure to inorganic mercury also can happen from drinking contaminated water and touching contaminated water and soil.

Other heavy metals to watch out for and look up include:

  • Aluminum (Al)
  • Antimony (Sb)
  • Barium (Ba)
  • Beryllium (Be)
  • Cobalt (Co)
  • Copper (Cu)
  • Iron (Fe)
  • Lithium (Li)
  • Manganese (Mn)
  • Molybdenum (Mo)
  • Nickel (Ni), Selenium (Se)
  • Silver (Ag)
  • Thallium (Tl)
  • Tin (Sn)
  • Uranium (U)
  • Vanadium (V)
  • Zinc (Zn)


Polycyclic Aromatic Hydrocarbons/PAH’s

Polycyclic aromatic hydrocarbons are a group of over 100 different semi-volatile organic compounds that are formed during the incomplete burning of coal, oil and gas, garbage or other organic substances like tobacco or charbroiled meat. PAHs are found in coal tar, crude oil, creosote and roofing tar, but a few are used in medicines or to make dyes, plastics and pesticides. When coal is converted to natural gas, PAHs can be released, which is why some former coal-gasification sites may have elevated levels of PAHs. They are also found in incinerators, coke ovens and asphalt processing and use. They are also a major concern when it comes to human and environmental health im- pacts at oil spills, as they are present in crude oil. Although hundreds of PAHs exist, two of the more common ones are benzo(a)pyrene and naphthalene. Polycyclic aromatic hydrocarbons can cause red blood cell damage that can lead to anemia; they can also suppress the immune system. Possible long-term health effects from exposure may include cataracts, kidney and liver damage and jaundice. Some polycyclic aromatic hydrocarbons are cancer-causing. Also, high prenatal exposure to PAHs is associated with lower IQ and childhood asthma, as well as low birth weight, premature delivery and heart malformations in babies.

Volatile Organic Compounds / VOC’s

According to the US Geological Survey, “many VOCs are human-made compounds of fuels, solvents, hydraulic fluids, paint thinners, and dry-cleaning agents commonly used in urban settings.” 3 These compounds evaporate very quickly, hence the word “volatile” in their name. At elevated concentrations, VOCs affect the cardiovascular, neurological and nervous systems, and many are known carcinogens. The following VOCs, present in oil spills and other industrial process- es, can pose a particular health risk to humans and the surrounding environment.


Benzene is a natural part of crude oil and gasoline, and is also used to make some types of rubbers, lubricants, plastics, dyes, detergents, drugs and pesticides. Industries that involve the use of benzene include the rubber industry, oil refineries, petroleum pipelines, coke and chemical plants, shoe manufacturers and gasoline-related industries and associated infrastructure. In most accidents and spills involving petroleum, benzene is definitely a concern. Natural sources of benzene include volcanoes and forest fires. Benzene is a known carcinogen and can cause a rare form of kidney cancer and leukemia as well as other blood cancers. Short-term inhalation of high levels of benzene can be fatal, and low levels can cause drowsiness, dizziness, headaches, tremors, rapid heart rate, confusion or mental fog and unconsciousness. Eating foods or drinking water contaminated with high levels of benzene can cause vomiting, stomach irritation, dizziness, sleepiness, convulsions and death. Benzene damages the bone marrow and can lead to a decrease in red blood cells and anemia. It can also cause excessive bleeding and depress the immune system, resulting in a higher incidence of infections. It can impact the reproductive systems of men and women and cause birth defects such as spinabifida and anencephaly. When animals have been exposed to benzenes in studies, results have shown low birth weights, delayed bone formation and bone marrow damage.

Ethyl Benzene

Ethyl benzene is found in coal tar and petroleum. It is used primarily to make the chemical styrene. It is used as a solvent, a constituent of asphalt and naphtha and is a constituent of synthetic rubber, fuels, paints, inks, carpet glues, varnishes, tobacco products and insecticides. It is a component of automotive and aviation fuels. Acute exposure to ethyl benzene can cause eye, throat, nose, upper respiratory tract, and mucous membrane irritation; chest constriction; redness and blistering of the skin. Neurological effects include dizziness, fatigue and lack of coordination. Animal studies have shown impacts to the central nervous system, pulmonary system and effects on the liver, kidney and eyes. Chronic exposure to ethyl benzene can cause fatigue, headache, and eye and upper respiratory tract irritation, as well as drying, dermatitis and defatting of the skin.


Toluene occurs naturally in crude oil. It is also produced in the process of making coke from coal and gasoline and other fuels (such as jet fuel) from crude oil. Toluene is used in making paints, paint thinners, fingernail polish, lacquers, adhesives and rubber and in some printing and leather tanning processes. Low to moderate exposure to toluene can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, loss of appetite and loss of hearing and color vision. Toluene is also know to impact the cardiovascular system and the neurological/nervous system. Higher exposure levels can cause un- consciousness and death.


Xylene occurs naturally in petroleum and coal tar; it can catch on fire easily. It is found in small amounts in airplane fuel and gasoline. It is used in paints, paint thinners and varnishes. It is used also as a solvent and cleaning agent, and in the printing, rubber and leather industries. Xylene exposure can damage the central nervous system, liver and other body systems. Signs and symptoms of acute exposure to xylene include headache, fatigue, irritability, lassitude, nausea, anorexia, flatulence, irritation of the eyes, nose and throat, issues with motor coordination and balance, flushing, redness of the face, a sensation of increased body heat, increased salivation, tremors, dizziness, confusion and cardiac irritability. Chronic exposure can cause central nervous system depression; conjunctivitis; dryness of nose, throat and skin; dermatitis; anemia; mucosal hemorrhage; bone marrow hyperplasia and kidney and liver damage.

Trichloroethylene (TCE)

TCE is used primarily as a degreasing agent for metal and electronic parts; as an extractant for oils, waxes and fats; a solvent for cellulose esters and ethers; a dry-cleaning fluid (although it has largely been re- placed since the 1950s by tetrachloroethylene); refrigerant and heat exchange fluid; fumigant; carrier agent in paints and adhesives; a scou- rant for textiles and as a feedstock for manufacturing organic chemicals. When first widely produced in the 1920s, its major use was to extract vegetable oils from plant materials such as soy, coconut and palm, as well as in coffee decaffeination. It has also been used in the medical field as an anesthetic. TCE can enter groundwater and surface water from industrial discharges or from improper disposal of industrial wastes at landfills. It can also be found in typewriter correction fluid, paint, spot removers, carpet-cleaning fluids, metal cleaners and varnishes.

When inhaled, TCE can cause central nervous system depression, liver and kidney damage. The symptoms of acute exposure can look similar to alcohol intoxication, beginning with a headache, dizziness and confusion and progressing with increasing exposure to unconsciousness. Respiratory and circulatory depression can eventually lead to death. TCE is believed to cause cancer (liver and kidney), leukemia, non-Hodgkin lymphoma as well as congenital heart defects.

There are many other VOCs (Tetrachloroethane, 1,2,4-Trichlorobenzene, Vinyl chloride) to be concerned about — those named above are just a few common ones. 

Persistent Organic Pollutants / POP’s

POPs are organic compounds that tend to persist in the environment for very long periods of time, where they biomaginify in the food chain and bioaccumulate in animals and humans. Because of this and their ability to travel through wind, air, soil and water, POPs are found all around the globe, even in places far from where they were produced. The main sources of POPs are the use of current or past pesticides and insecticides, as well as their use in industrial processes and in the production of pharmaceuticals, solvents, polyvinyl chloride and more.

As a result of POPs’ toxicity, by the 1980s many restrictions and bans on the production and use of POPs came into effect. Concentrations of some POPs have decreased substantially; however, the contaminants already in the environment continue to circulate, and there are still many countries where these chemicals are still being used as pes- ticides and in industrial processes. POPs are known to adversely affect the immune, reproductive, neurological, nervous, liver, skin and endocrine systems, as well as cause cancer. Even small exposures to POPs cause problems such as sterility and birth defects. Some POPs cause the body to become more chemically sensitive. Here are some common types of POPs.

Polychlorinated Biphenyls (PCBs)

PCBs have been used as coolants and lubricants in transformers, capacitors and other electrical equipment. Products made before 1977 that may contain PCBs include old fluorescent lighting fixtures and electrical devices containing PCB capacitors — and old microscopes, hydraulic oils and caulking agents. These compounds were also used in industrial and commercial products such as rubber products, plastics, plasticizers in paints and hydraulic equipment. Even after banning, PCB’s are released into the environment during their manufacturing process, from the improper disposal of products containing PCBs, from the incineration of some forms of waste or from leaks from electrical transformers. Because they are known to be very toxic, PCBs have been banned since the late 1970s in Canada and the USA and have been replaced in some cases by polybrominated diphenyl ethers (PBDEs). PBDEs also stay in our bodies for a long time, and can cause serious health problems such as damage to the brain and nerves.

Dioxins and Furans

Dioxins and furans are not intentionally manufactured, but form instead as byproducts of the manufacturing of other chlorinated chemicals, such as chlorinated wood preservatives and herbicides, and the chlorine bleaching of wood pulp for paper at pulp mills. These compounds may be generated by industrial processes or by combustion, including fuel burning in vehicles with leaded gasoline, municipal and medical waste incineration, metal smelting, open burning of trash, electrical transformer/capacitor fires and forest fires. Most dioxin is released when PVC plastic (commonly used to make pipes for water systems, as well as baby bottles, toys, food containers and other everyday products), bleached paper, coal, diesel fuel and other things that contain the chemical chlorine are burned. Dioxin is also released from metal smelting, cement making, papermaking and some pesticides. Dioxins and furans are not very mobile in the environment and tend to stick to soil and sediments. They can remain in soil for decades because they are incredibly slow to break down; they will be buried by accumulating sediments before they disappear.

Dichlorodiphenyltrichloroethane (DDT) and other Pesticides

DDT is one of the most notorious and well-known pesticides/insecticides. It has been banned in the USA and Canada since the 1970s, but its use continues globally. It is present at many waste sites and releases from these sites could result in environmental contamination. Most DDT in the environment is the result of widespread past uses and is still present due to its slow breakdown. Other pesticides are now used, but they also have some pretty serious impacts on the environment and on human health. Pesticides contaminate the environment through leaks from production facilities and storage tanks, runoff from sprayed fields, agricultural spraying and disposal.

Other POPs to be aware of include the following pesticides:

Aldrin, Alpha-hexachlorocyclohexane, Beta-hexachlorocyclohexane, Chlordane, Chlordecone, Dieldrin, Endosulfan, Endrin, Heptachlor, Hexachlorobenzene (HCB), Lindane, Mirex and Toxaphene.

The following industrial chemicals and byproducts are also POPs:

Hexabromobiphenyl (HBB), Hexabromocyclododecane (HBCD), Hexachlorobutadiene,Octabromodiphenyl ether,Pentabromodiphenyl ether (penta-BDE), Pentachlorobenzene, Perfluorooctane sulfonate (PFOS), Polychlorinated naphthalene (PCN) and short-chain chlorinated paraffins (SCCPs).


Radioactive materials can poison the food, land and water for many generations and centuries. One of the main ways that radiation gets into our environment is from the nuclear industry, through its mining operations, power plants and waste disposal. Uranium, plutonium, strontium, cesium, tritium and iodine (among others elements) can be released via radioactively-contaminated water, air emissions, waste and accidents.

Many radioactive materials are produced by the military (e.g. depleted uranium shells). Radiation exposure is most common where weapons are made, tested and used, such as military bases and war zones. Radioactive metals are also used in some products such as electronics. In oil and gas drilling, radiation can be introduced into the environment by extraction processes that leave behind waste containing concentrations of naturally occurring radioactive material (NORM) from certain soils and rocks. Radioactive wastes from oil and gas drilling can be found in produced water, drilling mud, sludge, slimes or evaporation ponds and pits. It can also concentrate in the mineral scales that form in pipes (pipe scale), storage tanks or other extraction equipment. Radionuclides in these wastes are primarily ra- dium-226, radium-228 and radon gas.

Radiation can cause cancer of the lungs, thyroid and blood, as well as diseases that affect the bones, muscles, nervous system, stomach and digestive system. Most exposure to harmful radiation occurs in small amounts over a long time, causing health problems to develop slowly. Nuclear accidents or explosions can cause death right away or within several weeks. People who survive six weeks after an explosion may recover for a while, but serious illness can return years later with many different forms of cancers and leukemia among other things. The effects of radiation can pass down from parents to children and grand- children, as birth defects, cancers and other health problems. Early signs of radiation sickness include nausea, vomiting, diarrhea and fatigue. These signs may be followed by hair loss, burning feeling in the body, shortness of breath, swelling of the mouth and throat, worsening of tooth of gum disease, dry cough, heart pain, rapid heartbeat, per- manent skin darkening, bleeding spots under the skin, anemia (pale or transparent skin, gums or fingernails) and death.