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Environment protection

The spraying environment is important in deciding what pesticide to use and how the pesticide should be applied.  The environment consists of:

• people carrying out the spraying
• people surrounding the spraying
• plants and animals in the field to be sprayed and surrounding it
• soil in the field and adjacent to it
• water in the field and in surrounding areas (above ground and underground)
• air surrounding the application

The spray operator must ensure that any action associated with the application of pesticides has a minimal effect on all of the above

Environmental Risk

The product toxicity and exposure to the environment determine the risk that a pesticide poses to the environment.

Product toxicity. The toxicity of the pesticide determines the potential for effecting the environment.  Each pesticide affects various parts of the environment in different ways.  Details on specific hazards are provided on the label.  The World Health Organization classification category ( I – IV) provides a general guide to toxicity for occupational health – see table below .  Only pesticides that pose a minimum risk to the environment are registered for use.  In the registration process companies must provide comprehensive data from laboratory and field studies to show that their product is safe for the intended crops (or species) and detail the impact on non-target environment (plants, animals soil, water and people).

Exposure

Exposure is a combination of the amount of product used and the number of times it is used. To minimize exposure, chemicals must be applied in accordance with the label directions and applied through properly calibrated equipment. This should  avoid overdosing and minimize wastage from over mixing.

Pesticide Movement in the Environment.

When a pesticide is introduced into the environment, many factors determine the ultimate fate of the pesticide. The fate processes fall into three broad categories:

• transfer,
• adsorption
• degradation

 

Transfer

A number of processes occur when a pesticide is applied to the target.   Some of these are essential for the pesticide to reach its target and work while others may be detrimental. These processes include:

• drift
• volatilization
• runoff
• leaching
• uptake

Drift is defined as the movement of the pesticide off target during or subsequent to the application operation.  Drift has been measured a number of kilometers from the application  site. There are 3 types of drift; droplet/particle drift, vapor drift and combinations of the two. Droplet/particle drift is the most common form with three types occurring: These are:

• direct wind drift
• thermal drift
• inversion drift

Small droplet size plays a role in all instances.

Volatilization is the conversion of the pesticide to a vapor.  This can occur during spraying before the pesticide reaches the target or subsequently after the pesticide has reached the target.  While the vapor pressure gives some indication of the rate of drift potential, the evaporation and movement in the air are more difficult to predict.  Atmospheric conditions such as wind speed and turbulence, and even plant characteristics have an influence.

Runoff occurs with water moving off the field carrying soil particles that contain the pesticide.  This process is responsible for the contamination of streams and waterways. Pollution of  streams has serious implications for fish and aquatic micro-flora and fauna, domestic stock and native fauna using these water sources.

Contamination of a watercourse can occur in a number of ways, including empty containers, direct spraying, drift and runoff or eroded sediments.  Runoff has the greatest potential to cause problems in the local environment.

In measurements in the USA, runoff losses of 1% of applied herbicides are common, with 5 to 10% loss of applied product occurring in catastrophic events.  

Ground cover, slope and time between application and the runoff producing event are important determining factors.

Leaching

Leaching of certain pesticides and fertilizer compounds to groundwater is becoming a serious environmental threat in parts of the USA and Europe.  The pesticides most at risk are those with high water solubility’s and low soil attraction, for example, chorsulfuron and dicamba.

Uptake

Uptake is the process where pesticides are taken into a plant or animal (target or non target) following contact with the pesticide.  For many pesticides such as the herbicide glyphosate absorption and translocation into the plant are critical for its performance.  Once absorbed the pesticide may be broken down by chemical reactions or may remain as a residue.  Factors that determine the adsorption process include :

• physical properties of the plant or animal
• chemical properties of the pesticide
• environmental conditions

Residues that may exist from pesticides applied during the crop growth phase either on the surface or internally may then be removed from the treatment site at harvest time.  The use of properly registered products in accordance with the label directions for the product minimizes downstream effect from this process.

Adsorption

Adsorption binds the pesticide to particles of soil or organic matter.  Adsorption is higher in dry clay soils that are high in organic matter.  Clay soils high in organic matter have more binding sites.  Dry condition increase binding because water in the soil competes for the binding sites.  Products such as paraquat , diquat, atrazine and glyphosate become strongly attached to clay particles.  In contrast, chorsulfuron and 2,4-D, which are repelled by soil particles are very soluble and move downwards in soil water solution. Following adsorption, if the product is not degraded plant back or residual problems can occur.

Degradation

Degradation processes responsible for breaking down pesticides include photo degradation chemical degradation and microbial degradation.  

Photodegradation. The actions of sunlight can breakdown pesticides that are on the surfaces of the soil and foliage.  The level of sunlight, the characteristics of the pesticide and the physical and chemical reactions between the pesticide and the surface of the foliage or soil affect the degradation process.

Chemical Degradation. The most common chemical reaction that breaks down pesticides is hydrolysis.  Factors such as pH, temperature, chemical and physical properties of the pesticide and its location affect the rate of degradation. Products that are broken down by this means include chorsulfuron and many carbamate and organophosphate insecticides.

Microbial Degradation. Microorganisms, such as fungi and bacteria, break down pesticides to produce food.  This process normally occurs in the soil.  Obviously, factors that determine microbial growth determine the rate of breakdown of pesticides.  These factors include temperature, aerobic status, pH, and water. Products that are broken down this way include 2,4-D and glyphosate.

Minimizing Environmental Contamination

All actions associated with the use and application of pesticides must be carried out in a manner to minimize contamination of the environment.  The important issues to minimize contamination are:

• store pesticides safely with appropriate emergency procedures in place
• select and use products that have a minimal effect on the environment ----
• READ the LABEL and follow the safety directions
• use application techniques that maximize the amount of product that reaches the target and minimizes the amount that moves off target
• dispose of pesticides and waste products in a safe manner.

Measuring Contamination

Measuring the amount of contamination provides data on the presence of a contaminant but not the effect of that contaminant.  With the use of more sophisticated scientific equipment the analytical sensitivity is becoming lower and lower.  This provides a large amount of data on the presence of contaminants but no information about the effect of the contaminant. The presence of pesticides in the environment can be measured:

• directly by chemical analysis of the soil, water, air or plant and animal tissue
• indirectly by bio assay using sensitive organisms
• indirectly by analyzing for indicators

The most widely found contamination is from the older generation products that are very persistent such as organochlorine pesticides such as DDT.

Repairing contamination

The techniques used to repair a contaminated site depend on the type and the level of the contamination.  Techniques that are used include:

• quarantining area
• identifying the source
• stop the exposure at the source
• change physical and chemical factors by using compounds such as lime on a spill at the mixing site.
• change microbial factors by using microbial breakdown to control for atrazine
• long-term changes to cultural practices i.e. Integrated Pest Management

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