Archive for the ‘Pesticides’ Category

It’s standard government policy to aerial and ground spray wherever gypsy moths are found, despite the fact that a 1994 BC Ministry of Forests (MOF) Report states: “The direct impact of an established gypsy moth population on BC’s natural resources would likely be small.”

The biocide of choice is a combination of 2.1 percent live bacteria, Bacillus thuringiensis (Bt), and 97.9 percent unknown chemicals which are kept hidden by the Trades Secret Act. Not even a physician, who may need this information to safely treat a victim of pesticide poisoning, is allowed to know what they are. This concoction is sprayed three or four times at 10-day intervals, usually beginning in mid to late April.

In 1996, the BC Environmental Appeal Board (EAB) stopped the Bt ground spraying of four blocks in New Westminster because it caused health reactions in other areas. These included skin rash and other immune, allergic and sensitization responses such as dry, itchy skin; red, burning eyes; dry, sore throat; cough and tightness in the chest.

The Board concluded that children were at greater risk from the effects of Bt than the general population. They also noted that no studies had been done on Bt to determine long-term effects. No spraying took place in New Westminster and despite predictions of a major infestation by government officials, the gypsy moth disappeared from the area and has not returned.

Two years later, the EAB stopped the aerial spraying of Victoria due to similar concerns:

“The panel finds that aerial spraying will create an unacceptable risk of health problems among the residents of these densely populated areas. In particular, the panel agrees with the appellants that there is a risk to the health of children, people of all ages who have allergies, asthma and other respiratory ailments, people with immune deficiencies, chemical hypersensitivities and the elderly. It also poses an unreasonable adverse effect to the environment (non-target species).”

Worldwide Bans

When Bt was sprayed in New Zealand in 1997, public health nurses noticed an increase in the number of premature births and miscarriages in the spray area. There were reports of as many as five miscarriages in one street alone. One of the women who miscarried is a registered nurse. She said she began wondering whether the spray was involved in her two miscarriages when four out of five friends who were pregnant about the same time and who lived in the spray area also miscarried.

Since the spraying began in New Zealand, an unusually high incidence of hypothyroidism in children has also been reported. The Ministry of Forestry in New Zealand has confirmed that the Bt spray harmed one in six households.

Any medical dictionary will confirm that Bt is a human pathogen. In fact, it can be fatal to people using anti-ulcer drugs. A few years ago, it was the cause of an outbreak of gastroenteritis in a chronic care facility in Ontario. According to a recent Medical Post article, French scientists called for a ban on Bt after finding that inhaled spores caused lung inflammation, internal bleeding and death in laboratory mice. It also destroyed tissue in the wounds of a French soldier in Bosnia and infected wounds in immunosuppressed mice.

In the Netherlands, scientists have discovered that Bt is capable of long-term survival in the environment. They found that Bt spores reproduced in both dead and living insects. Because Bt is so similar to Bacillus cereus (a bacteria that can cause food poisoning) and Bacillus anthracis (which can cause anthrax), Dutch authorities are calling for mandatory deoxyribonucleic acid testing before the release of this pesticide. Sweden has banned aerial spraying altogether.

The Society Targeting Overuse of Pesticides (STOP) is an international, privately funded research group. Their president, Christopher Lewis, points to government statistics which show that over the past 20 years in British Columbia, 80 per cent of detected introductions of gypsy moth have died out without any control measures. He also points to the 1994 MOF report which concluded that gypsy moths pose only a minimal risk to BC trees and would likely not establish here.

“This insect should be trapped or simply left alone,” says Lewis.

During the aerial Bt spraying of Vancouver in 1992, a 10 per cent sample of emergency department visits found 1,839 patients with discharges from eyes or respiratory tract; 1,352 with respiratory problems; 100 with rashes; 60 with unexplained allergic reactions; and 119 with nosebleeds. It’s important to remember that the potential exists for 10 times these numbers. (There was another health report completed by the Capital Health Region in Victoria following gypsy moth spraying in 1998. However, it was decried by critics as a whitewash and did not go into the number of emergency room visits the way the 1992 study did.)

Under a 1995 directive from the US Environmental Protection Agency (EPA) workers cannot enter an area sprayed with Bt for at least four hours. And, one of the new EPA registration requirements for Bt pesticides is that workers coming in contact with the spores must wear a special respirator.

In the US it’s a violation of federal law to claim that pesticides are safe when used as directed. And, a Health Canada directive has made it illegal to claim that a pesticide is “safe,” “natural” or “organic.”

The BC government insists that it cannot sell BC lumber internationally unless the spraying is done, regardless of human health hazards, because international markets will not accept the lumber. This policy has not been changed in recent World Trade Organization agreements.

For an in-depth analysis of Bt pesticides visit the STOP website at vcn.bc.ca/stop.


Paula Linquist is a writer, particularly interested in environmental issues. She lives in North Vancouver, BC.


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What Happens to Pesticides

When a pesticide is released into the environment many things happen to it. Sometimes what happens is beneficial. For example, the leaching of some herbicides into the root zone can give you better weed control.

Sometimes, releasing pesticides into the environment can be harmful, as not all of the applied chemical reaches the target site. For example, runoff can move a herbicide away from target weeds. The chemical is wasted, weed control is reduced, and there is more chance of damaging other plants and polluting soil and water. Or some of the pesticide may drift downwind and outside of the intended application site.

Many processes affect what happens to pesticides in the environment. These processes include adsorption, transfer, breakdown and degradation. Transfer includes processes that move the pesticide away from the target site. These include volatilization, spray drift, runoff, leaching, absorption and crop removal.

Each of these processes is explained in the following sections.

Environmental degradation of pesticides

Transfer Processes
Adsorption is the binding of pesticides to soil particles. The amount a pesticide is adsorbed to the soil varies with the type of pesticide, soil, moisture, soil pH, and soil texture. Pesticides are strongly adsorbed to soils that are high in clay or organic matter. They are not as strongly adsorbed to sandy soils.Most soil-bound pesticides are less likely to give off vapours or leach through the soil. They are also less easily taken up by plants. For this reason you may require the higher rate listed on the pesticide label for soils high in clay or organic matter.

Volatilization is the process of solids or liquids converting into a gas, which can move away from the initial application site. This movement is called vapour drift. Vapour drift from some herbicides can damage nearby crops.

Pesticides volatize most readily from sandy and wet soils. Hot, dry, or windy weather and small spray drops increase volatilization.

Where recommended, incorporating the pesticide into the soil can help reduce volatilization.

Spray Drift is the airborne movement of spray droplets away from a treatment site during application.

Spray drift is affected by:

  • spray droplet size – the smaller the droplets, the more likely they will drift
  • wind speed – the stronger the wind, the more pesticide spray will drift
  • distance between nozzle and target plant or ground – the greater the distance, the more the wind can affect the spray

Drift can damage nearby sensitive crops or can contaminate crops ready to harvest. Drift may also be a hazard to people, domestic animals, or pollinating insects. Drift can contaminate water in ponds, streams, and ditches and harm fish or other aquatic plants and animals. Excessive drift also reduces the pesticide applied to the target and can reduce the effectiveness of a treatment.

<!–Ways to reduce spray drift are discussed in the Drift Management section of the Environmental Protection heading on this website.

–>Runoff is the movement of pesticides in water over a sloping surface. The pesticides are either mixed in the water or bound to eroding soil. Runoff can also occur when water is added to a field faster than it can be absorbed into the soil. Pesticides may move with runoff as compounds dissolved in the water or attached to soil particles.

The amount of pesticide runoff depends on:

  • the slope
  • the texture of the soil
  • the soil moisture content
  • the amount and timing of a rain-event (irrigation or rainfall)
  • the type of pesticide used

Runoff from areas treated with pesticides can pollute streams, ponds, lakes, and wells. Pesticide residues in surface water can harm plants and animals and contaminate groundwater. Water contamination can affect livestock and crops downstream.

Pesticide runoff can be reduced by:

  • using minimum tillage techniques to reduce soil erosion
  • grading surface to reduce slopes
  • diking to contain runoff
  • leaving border vegetation and plant cover to contain runoff

Pesticide losses from runoff are greatest when it rains heavily right after you spray. Reduce the chances of runoff by watching the weather forecast. If heavy rain is expected, delay spraying to avoid runoff. Irrigate according to label instructions.

Leaching is the movement of pesticides in water through the soil. Leaching occurs downward, upward, or sideways. The factors influencing whether pesticides will be leached into groundwater include characteristics of the soil and pesticide, and their interaction with water from a rain-event such as irrigation or rainfall. These factors are summarized in the table below.

Leaching can be increased when:

  • the pesticide is water soluble
  • the soil is sandy
  • a rain-event occurs shortly after spraying
  • the pesticide is not strongly adsorbed to the soil

Groundwater may be contaminated if pesticides leach from treated fields, mixing sites, washing sites, or waste disposal areas.

Summary of Groundwater Contamination Potential as Influenced
by Water, Pesticide and Soil Characteristics
Risk of Groundwater Contamination
Low risk
High risk
Pesticide characteristics
Water solubility low high
Soil adsorption high low
Persistence low high
Soil characteristics
Texture fine clay coarse sand
Organic matter high low
Macropores few, small many, large
Depth to groundwater deep
(100 ft or more)
(20 ft or less)
Water volume
Rain/irrigation small volumes at infrequent intervals large volumes at frequent intervals
Based on: McBride, D. K. 1989. Managing pesticides to prevent groundwater contamination. North Dakota State University Extension Service, Publication E-979.

Similar factors influence pesticide movement in surface runoff, except that pesticides with low water solubility may move with surface runoff if they are strongly adsorbed to soil particles and have some degree of persistence.

Soil characteristics are important to pesticide movement. Clay soils have a high capacity to adsorb many chemicals including pesticides and soil nutrients. Sandy soils have a much lower capacity to adsorb pesticides. Organic matter in the soil also can adsorb pesticides. Soil structure influences the movement of water and pesticides. Coarse textured sandy soils with large air spaces allow more rapid movement of water than fine textured or compacted soils with fewer air spaces. Other characteristics of the site, such as depth to groundwater, or distance to surface water, are important. Finally, the pattern of water falling on the soil through irrigation or rainfall is significant. Small volumes of water at infrequent intervals are less likely to move pesticides than large volumes of water at more frequent intervals.

Absorption is the uptake of pesticides and other chemicals into plants or microorganisms. Most pesticides break down once they are absorbed. Pesticide residues may be broken down or remain inside the plant or animal and be released back into the environment when the animal dies or as the plant decays.

Some pesticides stay in the soil long enough to be absorbed by plants grown in a field years later. They may damage or leave residues in future crops.

Crop Removal through harvest or grazing may remove pesticide residues.

Degradation or Breakdown Processes
Degradation is the process of pesticide breakdown after application. Pesticides are broken down by microbes, chemical reactions, and light or photodegradation. This process may take anywhere from hours or days to years, depending on environmental conditions and the chemical characteristics of the pesticide. Pesticides that break down quickly generally do not persist in the environment or on the crop. However pesticides that break down too rapidly may only provide short-term control.Microbial breakdown is the breakdown of chemicals by microorganisms such as fungi and bacteria.

Microbial breakdown tends to increase when:

  • temperatures are warm
  • soil pH is favourable
  • soil moisture and oxygen are adequate
  • soil fertility is good

Chemical breakdown is the breakdown of pesticides by chemical reactions in the soil. The rate and type of chemical reactions that occur are influenced by:

  • the binding of pesticides to the soil
  • soil temperatures
  • pH levels – Many pesticides, especially the organophosphate insecticides, break down more rapidly in alkaline soils or in spray tank water with a high pH level.
  • moisture

Photodegradation is the breakdown of pesticides by sunlight. All pesticides are susceptible to photodegradation to some extent. The rate of breakdown is influenced by the intensity and spectrum of sunlight, length of exposure, and the properties of the pesticide. Pesticides applied to foliage are more exposed to sunlight than pesticides that are incorporated into the soil. Pesticides may break down faster inside plastic-covered greenhouses than inside glass greenhouses, since glass filters out much of the ultraviolet light that degrades pesticides.


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