Pesticides

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Pesticides are used to control weeds, pests and diseases in crops (including grassland). It is normal practice for several different pesticides to be applied to a single crop in any given growing season.

CLICK HERE for links to Crop Protection Association with information on pesticides.

 

Pesticides in the UK

Different farming practices require a range of pesticides. The chart below indicates  the area of land treated in the UK. This is calculated by multiplying the area treated by the number of spray types it receives, e.g. a tank mix of two different chemicals spread seven times a season would be equivalent to 14 times the area sprayed. 

 

                Source: Central Science Laboratory from Environment Agency website                  

It can be observed that spray area has increased over time owing to:

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More frequent treatments

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More complex tank mixes

This, however is not necessarily a negative factor, as it could reflect:

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The use of less persistent compounds

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Lower rates of application

Legislation and safety

CLICK HERE  for the 1998 Pesticides act

CLICK HERE   for UK Pesticides Safety Directorate (now part of the UK Health and Safety Executive)

 

A number of EU countries have specific reduction programmes concerning the quantities of pesticides applied or sold. However measuring the amount of pesticides used or sold is not necessarily a good indicator of adverse environmental effects. The quantity used is significant, but the toxicity of the average ingredients and the way the pesticide is used will also influence the risk.

 

            Source: Central Science Laboratory, pesticide usage statistics          

 

The chart above shows figures for sulphuric acid and all other pesticides excluding sulphuric acids.  Sulphuric acid is used to kill potato haulms (tops) prior to harvest. Since it is applied in very high doses for each area treated, the pattern of its use tends to distort the overall picture. Sulphuric acid on potatoes currently accounts for 33% of total UK pesticide use by weight.

 

Pause for thought.........List 5 factors that will effect the future area of land treated with pesticides in the UK. 

 

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Pesticides in water

The river on the left and the lake on the right exhibit a wide range of aquatic fauna and flora.

 

Recent amendments to EC pesticide legislation require pesticide products to meet standards of a maximum level of 0.1 g/l for potential contamination of groundwater. The graph below reflects the percentage of sites where at least one sample was found to exceed these limits.

 

 

Source: Environment Agency (1998)                

 

             

Where excesses do occur, these are found to be in very small quantities. Although the graph above does show variations between years, underlying data suggests that it is not indicative of any trend, but reflects changes in sampling variation and protocol. For the latest figures on the levels of pesticides CLICK HERE for the Environment Agency website

 

Fresh water

 

There are currently around 350 ingredients approved for use in agricultural pesticide products in the UK.  Most pesticides detected in freshwater (as opposed to ground water), are found in very low concentrations that are well within existing or proposed Environmental Quality Standards (EVQ's). The very low limit set by the EC Drinking Water Directive (1g/l or 1 part per 10 billion) has been used as a benchmark. The graph below gives details for five herbicides and one insecticide with respect to limit exceedance, these are the types most commonly found in rivers. The insecticide 'Lindane' has been included , owing to its very high toxicity to aquatic life.

 

Source: Environment Agency (1998)     

 

Pause for thought........ State 5 factors which may lead to limit exceedance in water samples 

  

The marked annual variations can often reflect weather patterns and usage, the percentage of Isoproturon samples exceeding limits remains significant reflecting its very high use in cereal production. The number of samples containing high levels of Atrazine has fallen significantly since 1992.

 

Government policy dictates that the amount of pesticides used should be limited to the minimum necessary for the effective control of pests. 

  

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Factors effecting pesticide pollution of soil, water and air

Drainage:

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Farmland is often well drained and natural drainage is often enhanced by land drains

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Water from excessive rainfall and irrigation cannot always be held within the soil structure

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Therefore pesticides and residues (also nitrates and phosphates) can be quickly transported to contaminate ground water and fresh water supplies over a large geographical area

Water flow is increasingly controlled and culverted

The pesticide:

Individual pesticides have unique properties, and many variable factors determine the specific risk in terms of water pollution:

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Pesticide half-life: The more stable the pesticide, the longer it takes to break down. This can be measured in terms of its half life, the longer it takes to break down , the higher its persistence. The half life is unique to individual products but variable depending on specific environmental and application factors.

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Mobility in soil: All pesticides have unique mobility properties, both vertically and horizontally through the soil structure. Residual herbicides applied to directly to soil are designed to bond to the soil structure.

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Solubility in water: Many pesticides are soluble in water out of necessity so that they can be applied with water and be absorbed by the target. The higher the solubility of the pesticide, the higher the risk of leaching. Residual herbicides are generally of lower solubility to aid soil binding but their persistency in the soil can cause other problems.

Other Factors:

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Rainfall: High levels of rainfall increases the risk of pesticides contaminating water. Movement into water courses occurs directly by washing from pest and target areas into drains after rainfall. It can also occur within the soil structure by displacement of pesticide from absorption sites by water and on treated soil which has moved to water through soil erosion.

 

Source: Environment Agency (1995) 

 

Pause for thought....... what relationship does the above graph suggest and what processes would be involved?    

 

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Microbial activity: Pesticides in the soil are primarily broken down by microbial activity. The greater the microbial activity, the faster the degradation. Loss of pesticide residues can also occur by evaporation and photodecomposition.

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Soil temperature: Soil microbial activity and pesticide breakdown is largely linked to soil temperature

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Treatment surface: Pesticides such as residual herbicides  applied to hard surfaces such as concrete or tarmac (i.e. garden pathways and driveways) have nothing to be absorbed by and are particularly vulnerable to movement into water courses and non target areas, especially after rainfall. These risks are greatly reduced when the pesticide is applied to soil. Hence, pesticides in water can often be the result of non agricultural usage

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Application rate: The more pesticide that is applied, the longer significant concentrations remain

 

Indirect effects of pesticides

 

The indirect effects of pesticides in the food chain are discussed in subject 4 (species decline).

 

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Pesticides - food and health

 

The current consensus of opinion is that pesticides are present at such low levels that they pose no threat to human health.

 

Pause for thought........Read the quotes below and then follow outside link to BBC news articles and assess whether they have influenced your prior opinions

 

All food is a collection of chemicals. There is a vast number of natural ones, about which we know very little, or a relatively few synthetic ones about which we know a lot. British Agrochemicals Association

 

It is said that 'When standing on a city street in the UK, you are never more than  seventy feet away from a rat'. Whether strictly true or not, it does highlight our continued need to fight pests and vermin which can cause ill health. ICI Agro Chemicals Division

 

The pesticides we are eating are naturally 99.99% occurring. Dr Bruce Ames, Chairman, Department of Biochemistry, University of California

 

I would rather go into a supermarket and find a tenth part per million of a certain pesticide on apples or lettuce, than to find a cockroach that is carrying 40 or 50 disease organisms on its feet, crawling over the lettuce. Ben Kentack, State Entomology Advisor, South Dakota

 

Today the major safety issue is microbial contamination, where the risks are estimated to be 100 000 times greater than the risks associated with pesticide residues.  Prof. Will Waites, Nottingham University

 

What we have to face is not an occasional dose of poison which has accidentally got into some article of food, but a persistent and continuous poisoning of the whole human environment. (Rachel Carson, Silent Spring, 1962)

 

Approved pesticide store (left). The dead pike on the right could have been killed by pesticides, pollution or even a fisherman

 

CLICK HERE for BBC online information regarding pesticides and human health, contains links to various news articles

CLICK HERE  for Local Environmental Risk Assessment for Pesticides (LERAP), these pages include rules regulations, categories and instructions on how to carry out a LERAP and details of buffer zones.

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