Pesticide Contamination of Farm Water Supplies: Recommendations on Avoidance, Cleanup and Responsibilities

Agdex#:	607
Publication Date:	December, 2000
Order#:	00-099
Last Reviewed:	October, 2004
History:	Replaces OMAF Factsheet, Pesticide Contamination of Farm Water Supplies, Order No. 86-077
Written by:	Dr. Richard Frank - OMAF; K. R. Wilson - OMAF

Table of Contents

1. Introduction
2. Farm Families
3. Mode of Contamination
   • Direct Contamination
   • Indirect Contamination
4. Water Quality
5. The Pesticides Act and Regulation 914
6. Water Sources
7. In Case of a Pesticide Spill
8. Recommendations
9. Decontamination of Water Supplies
10. Summary
11. Other Information
12. Related Links

Introduction

A large volume of water is taken every year from farm wells, ponds, ditches and streams to apply pesticides to crops and livestock. From time to time, accidental contamination of the water sources occurs. Contamination of surface waters is an indictable offence under provincial legislation (or statutes) including the Pesticides Act, the Water Resources Act, and the Environmental Protection Act. If fish are killed as a result of the contamination the federal Fisheries Act is also violated.

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Farm Famililes

Keep a separate well for drinking purposes only.

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Mode of Contamination

When the contamination of a stream, pond or well occurs, it is usually due to one of the following.
1. Direct Contamination

• Spillage of pesticide concentrate when mixing and loading sprayers
• Leakage of stored concentrate or discarding unrinsed 'empty' containers in or near to a water supply
• Back siphoning or overfilling of sprayer tanks
• Rinsing or washing spray equipment, and
• Spray drift under windy conditions or application too close to open water.

2. Indirect Contamination

• Movement of pesticide from treated land by heavy rains and runoff waters, and
• Spills that leak to groundwater and move laterally in aquifers.

Direct Contamination

Careless Handling of Concentrates

Examples of careless handling include:

• pesticides stored near water supply areas leak from corroded containers to contaminate reservoirs, wells and ponds
• concentrate from dropped or fractured containers spills, and leads to serious contamination of private water supplies
• unrinsed empty containers are left in or near streams, or in dried up ditches that subsequently carry runoff waters. This contaminates surface water.

Filling Spray Rigs

Accidents while filling spray equipment often result in water contaminations that are hazardous to human and livestock health. Residues in well waters can be up to 500 times higher than concentrations caused from spray drift or indirect contaminations. These accidents usually involve the back siphoning from spray equipment directly into the well and the overfilling of tanks which potentially create spills in and around the well head. In porous soil, pesticides can readily leak into the groundwater and contaminate the well. On clay soils, rains can readily wash the contaminated surface soil into the well. In either case, the well can be contaminated for a long period of time.

Pesticide Spray Drift

Usually this type of water contamination results in very low residue concentrations. The greatest danger exists when spraying is carried out close to wells or surface water. Under normal spraying conditions and using low pressure application, drift is confined to 5-10 m down wind (at wind speeds less than 11 km/h). To avoid contamination, leave a buffer zone of at least 10 m between all water supply sources and sprayed areas. Consult the LABEL for specific instructions on buffer zones and the specified distance between the water source and sprayed areas before applying a pest control product.

Indirect Contamination

Surface Runoff

Surface runoff waters pick up soil particles and pesticides from treated fields or spills, and carries these into streams, ditches, ponds and wells. This normally occurs when heavy rains follow within a few days of a spray operation, although it can also happen any time of the year with pesticides that persist in soil year round. In studies on 11 watersheds, over 60% of the atrazine contaminations entered streams with surface runoff waters and more than half of this was during snow melt and spring rains. By contrast contamination with metribuzin and 2,4-D occurred only within a few hours or days of the spraying of the crop or rights-of-way.

The greatest loss occurs when rains fall within 24 hours of application. Removal of pesticides from the soil surface decreases with time following application and is usually negligible one week after spraying.

Runoff is normally more severe on clay soils and less of a problem on sandy soils.

Subsurface Drainage Water

Pesticides that are persistent and water soluble will move through the soil and into the water table. In a study on 11 streams, atrazine, simazine and endosulfan were found in tile drainage waters. In studies on muck soils, diazinon was found in drainage waters within a few days of use.

Most often the subsurface contaminations are the result of spills of formulated concentrates that reach groundwater. In Ontario this has been observed with amitrole, and picloram. Seepage of such groundwater may reach wells and streams.

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Water Quality

Where waters are used for irrigation purposes, residues of herbicides should be at or below 0.1 ug/L. Crop injury has been observed with herbicides above this concentration. In the case of picloram and dicamba, residues below the detection limit have caused injury to greenhouse plants where repeated use of the water has occurred.

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The Pesticides Act and Regulation 914

The Pesticides Act and Regulation 914 contain many references to pesticide contamination of public waters as being an offence in Ontario. The Ontario Ministry of the Environment administers the Pesticides Act and Regulation 914. Following are the main sections concerning pesticide spills and contamination:

• Under Section 4 of the Act, no person shall permit the deposition, addition, emission or discharge of a pesticide into the environment that causes: (a) impaired quality; (b) injury or damage to property or plant and animal life; or (c) adverse health or discomfort to any person greater than would necessarily result from the proper use of the pesticide.
• Under Regulation 914 s.25 (1) no person shall use water from a lake, river or other surface water for spray operations unless the equipment is fitted with an effective device to prevent backflow.
• Under Regulation 914 s.25 (2) no personal shall wash any equipment used to perform a spray operation so that the pesticide directly or indirectly is deposited into any lake, river or other surface water.
• Under Regulation 914 s.27 persons responsible for pesticide use shall dispose of the container and its contents in such a manner that they are not near a watercourse or water table, and clean up any spillage and decontaminate the area that has come into contact with the pesticide.

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Water Sources

Stream Water

Contaminating streams is an offence under the provincial Pesticides Act and the federal Fisheries Act, particularly if a fish kill accompanies the pesticide contamination. When the contaminant is a pesticide such as rotenone or endosulfan, highly visible fish kills may result. When a herbicide is involved, the water may cause problems when used for irrigation, especially in greenhouse production of highly sensitive plants such as tobacco or tomato seedlings. Stream waters are used as potable waters in several communities in Ontario and contamination can pose a hazard to human health. Water is also drawn from streams for livestock use and can pose a hazard to livestock and the quality of their produce.

Farm Ponds and Wells

Similar effects are observed in farm ponds where fish are killed and crops damaged. When well waters are contaminated, losses of plants in greenhouse production can be particularly severe. Samples of well water have been analyzed when nausea has occurred in farm families. The water can also develop off-flavours and become objectionable to drink.

Indirect Contamination

Concentrations of pesticide in water from indirect contaminations are generally low; however, they may continue over an extended period. This is especially the case when subterranean contamination has occurred in an aquifer. Depending on the pesticide involved, it can cause problems when the water is used to raise plants in greenhouses.

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In Case of a Pesticide Spill

• Remove all persons and animals from the spill area. Exercise extreme caution in entering a contaminated area and wear adequate personal protective equipment. Remember to protect yourself first in an emergency situation.
• Apply the general principals of first aid, such as basic life support procedures. Remove contaminated clothing. Thoroughly wash affected skin areas with soap and water.
• Isolate the area so that no unauthorized person, animal or vehicle is exposed or contaminated by accidentally walking into or moving through the spill, or is exposed to fumes from the pesticide. Establish a decontamination line around the perimeter such that anyone entering the area must be wearing adequate protective equipment; and persons and/or vehicles leaving the spill area can be decontaminated.
• Contain the spread of the pesticide to prevent further contamination of the environment, in particular watercourses, reservoirs, and wells. If possible, stop the continued leaking of a container. Construct a barrier to soak up the pesticide made of soil, sawdust, newspaper; or soil, sawdust, activated charcoal, vermiculite, and pet litter.
• Immediately notify the Spills Action Centre of the Ministry of the Environment by calling 1-800-268-6060. Important information can be obtained from the distributor or registrant of the pesticide product or the emergency response system for dangerous goods - CANUTEC - (Ottawa 613-996-6666).
• Clean up the spill area. Pump surplus liquid product into drums. Soak up small amounts of liquids in sawdust, soil or other absorbent. For dry powder or granular product lightly wet or sprinkle with damp soil or sawdust. Then shovel this material into a drum. If the spill occurs on the ground, it may be necessary to dig up the contaminated area and place the soil in drums. Place leaky or damaged containers in a drum or heavy plastic bag. Inside a building ventilate the area to prevent the build up of toxic fumes.
• If possible, decontaminate the spill area. After removing the spilt pesticide, soak the contaminated area with a mixture of equal parts of bleach and water. A dike placed around the spill area will prevent the spread of the decontamination solution. Caustic soda or lye in water may be used instead of bleach. Then, without removing the chemicals, spread hydrated lime over the entire area and leave for 1-2 hours. After this period shovel the material into drums. Repeat the application of bleach in water (1:1 ratio) over the entire area and allow to stand for a further 30 minutes. Then hose down the area with water and a detergent as final cleanup. Consult the label for specific instructions on decontamination since not all pesticides are detoxified by the above procedures.
• Decontaminate all equipment used in the cleanup, as well as vehicles contaminated by the spill. Follow the same procedures.
• Cover and label drums containing the cleanup material. Labels should read "Pesticide - Poison" and include trade name(s) or common name(s). Transport drums using a licensed waste hauler to a disposal site approved by the Ministry of the Environment.
• All workers must take a shower, and change to clean clothing. Wash all clothing, boots, gloves, etc. with soap and water before reuse.

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Recommendations

Pesticide Storage

Keep pesticide concentrates away from unauthorized persons. Always keep in original containers in a locked storage area. Make sure pesticides storage areas are away from water supplies and above high water flood levels.

Spray Equipment

Anti-back flow devices must be used on all equipment where water is being drawn from surface or well waters. Fill spray tanks and move away from the source of water before adding the toxicant to the spray equipment. A minimum distance of 30 m is recommended. Using nurse tanks for water supplies and automatic metering devices to add the toxicant can greatly reduce the possibility of contamination of water supplies. Problems often arise because the filling and mixing operations are left unattended.

Pesticide Containers

Using clean water, triple or jet-rinse all empty containers made of metal, plastic or glass. Add the rinsings to the sprayer tank. Other appropriate solvents may also be used. Once thoroughly rinsed, take containers for recycling to either a Pesticide Container Recycling Depot or an approved waste disposal site. [Reg.914, s.27]

All empty paper or cardboard containers can be disposed of by:

• triple- or jet- rinsing (if possible) using clean water; and either burning, (if allowed by municipal by-laws) in circumstances that persons and animals are kept out of any resultant smoke and any resultant smoke is directed away from buildings, highways, roads or outdoor areas frequented by the public, or
• taken to an approved waste disposal site [Reg.914, s.27].
  

Spray Operations

Deposition of spray drift into stream water is largely due either to spraying too close to surface waters or spraying when the wind is too strong. Cover wells if spray operations are to be carried out in their vicinity. Do not spraying when winds exceed 11 km/hr. Set back distances of 5-10 m are recommended.

Runoff Water

Heavy rains leading to runoff waters carry pesticides into streams, ponds and wells. To reduce these pesticide losses from treated fields located along streams and ponds, consider planting across the slope. Buffer zones of 5-10 m can reduce losses on relatively flat land but help little on sloping land. Incorporating into the soil or foliar application after crop emergence results in lower losses than applying to bare soil.

Stream and Farm Ponds

The location and protection of a farm pond is important. If the pond is to be located where surface waters can run off treated fields, reduce contamination by berming, ditching or having a grassed buffer strip between the pond and the treated area.

General recommendations on controlling soil erosion help reduce the loss of pesticides to ditches and streams.

Farm Wells

Protect wells against surface runoff waters by berming. There are no adequate means of preventing contamination from subterranean seepage. Construct wells for drinking water purposes in accordance with Ontario Ministry of the Environment guidelines. This will greatly reduce the risk of contamination.

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Decontamination of Water Supplies

Streams and Ponds

Little can be done to decontaminate streams or ponds, and only time will effect breakdown of the pesticide. In general, the length of time depends on:

• the pesticide
• the time of year
• the extent of the spill or contamination.

Removing empty containers or contaminated soil can improve the speed of cleanup and are required under the Pesticides Act.

Farm Wells

Emptying the well of water, several times, may be adequate to decontaminate the water supply if low amounts of toxicant have entered the well as spray drift. More often the bottom of the well must be scraped and the sediment removed. Well waters are quite cold and often alkaline. Most pesticides are less soluble under these conditions than in waters at higher temperatures and at a neutral pH. Often the toxicant is spilled down the sides of the well and hence removal must include washing the walls, if stone or cement, or scraping if they are earthen, in order to affect a cleanup. This would be followed by emptying the well frequently over several days, weeks or months and releasing the water at least 30 m from the well.

When the contamination involves a spill around the lip of the well, remove the contaminated surface soil. Where only water is removed from the well, decontamination can take from 6 months to 3 years, and in some cases the well has to be abandoned. Cleanup has been rapid where the well was decontaminated by scraping and removing water. Activated charcoal filters are available for decontaminating water when installed on a drinking water line. These filters have been effectively used in the United States, and are currently being tested in Ontario. Problems of bacterial infection can occur with these devices.

Where a large quantity of toxicant is spilled close to the well, especially on sandy or gravelly soils, the pesticide may soak deep into the soil and seep into the well in succeeding years during the spring melt or under heavy rainfall conditions. This has occurred with compounds such as dinoseb and amitrole that are highly soluble. Where this has occurred the well has had to be abandoned. With subterranean contamination, wells cannot be decontaminated and abandonment is the only recourse.

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Summary

Protect Water Supplies

It is an offence to contaminate surface waters with pesticides.

• Always read the label before you apply any pesticide product.
• Keep concentrates above floodplain in a locked storage.
• Triple-rinse, and properly dispose of empty pesticide containers.
• Mix concentrates and water 30 m away from water supply.
• Use appropriate buffer zones and berms to avoid surface water contamination by spray drift or runoff waters.
• Draw drinking water supplies from a separate well.
  
• Do not spray within 10 m of shallow wells or 5-10 m of other water supplies.

Related Links

• Health Canada
• Ontario Ministry of the Environment
• International Joint Commission
• Ontario Ministry of the Environment administers the Pesticides Act and Regulation 914
• Ontario Pesticide Container Recycling Program