ANNEX A1: Pesticide Tax Proposal - The Environmental Risks Of Pesticide Use
Introduction
Pesticides are one of many tools available to farmers as part of their crop production system. Their effects in controlling pests and diseases prevent the loss of yield and quality over a wide range of arable, fruit and vegetable crops. Some products have additional use in industrial, amenity and home and garden situations and there are allied uses for some products for the treatment of pests on animals. They have undoubtedly made a significant contribution to food production over the past 40-50 years or so.
However, by definition, all chemical pesticides are designed to kill a particular class of organism and the state of the art is such that selectivity to specific target organisms has seldom been achieved. Furthermore, they are deliberately released into the environment over wide areas of land. This means that the majority of products will pose some risk of damage to non-target organisms in the environment even though an environmental risk assessment forms part of the registration process. The pesticide approval process is in place to prevent materials with unacceptable risks to the environment (and to humans) from reaching the market place but it cannot prevent all risks.
Because the use of pesticides poses a risk to the environment, successive governments have pursued a policy to minimise the use of pesticides consistent with effective pest control. In addition to the regulatory process the minimisation policy is supported by a code of practice for farmers and an extensive research and development programme. Additionally the Pesticide Forum, which brings together farming and environmental interests, has developed an Action Plan for the Responsible Use of Pesticides. The proposed tax or charge could complement these initiatives.
Types of pesticide impact
All agricultural activities change the natural environment and pesticides are, therefore, used in an environment which has already been modified by human activity. The environmental impact of pesticides as such could be defined as the incremental effects on wild, non-target plants and animals over and above those caused by the agricultural activity itself. However, agricultural practices are themselves modified as a result of the availability of pesticides and it is therefore not easy to segregate out the impacts specifically caused by pesticides.
There are a number of ways in which pesticides can have an impact on the environment and on non-target wildlife in particular. These are:
direct effects on non-target species of approved use; this includes both lethal and sub-lethal effects, including primary and secondary poisoning, both acting within the crop and off-target (eg in water courses). It includes the effects of pesticides alone and in combination with other pollutants.
indirect effects of approved use, for example through reduction in food availability to non-target species or deterioration in habitat quality.
the occurrence of pesticides in Controlled Waters at concentrations exceeding those defined by Environmental Quality Standards (EQSs) and the EC Drinking Water Directive.
misuse of pesticides - negligent or incorrect use can lead to inadvertent damage to wildlife.
the abuse of pesticides - deliberate use of certain pesticides to poison wildlife in contravention of conditions of use.
Direct effects of approved use
There are a number of examples of the approved use of pesticides having a direct effect on non-target species. There have been several recent cases, for instance, of secondary poisoning of birds of prey by anticholinesterase insecticides. Of particular nature conservation concern are incidents involving species of bats. These are frequently associated with timber treatment of roosting or maternity sites, and have included organochlorine, OP and pyrethroid insecticides. At present there is little evidence that such direct impacts on vertebrate species are having population effects although species of conservation importance have been involved and continue to be at risk from incidents involving direct effects. Seed treatments must be considered a potential hazard, especially if environmental conditions encourage greater feeding on dressed seed, since there is some evidence that birds may be exposed to levels that can give rise to lethal or sub-lethal toxic effects.
There is a need to remain vigilant, especially in areas concerning:
wildlife groups which are not, or are poorly monitored, particularly aquatic macrophytes and invertebrates and non-target terrestrial invertebrates other than bees;
routes of secondary poisoning through approved use of insecticides;
sublethal or chronic effects;
interactive or synergistic effects.
Sub-lethal effects may increase the susceptibility to other mortality factors (such as predation) as well as reducing reproduction success. Whilst exposure to anti-cholinesterase pesticides and consequent inhibition of cholinesterase activity is well documented for a range of wildlife, population effects have not been demonstrated as a consequence of such sub-lethal effects in the UK. Elsewhere, there is evidence for the serious consequences of these effects and in North America exposure of song birds to OPs during forestry spraying operations has been demonstrated to reduce reproductive success in the field. Prediction of risk to non-target vertebrate species in the case of anticholinesterase insecticides needs to be particularly rigorous, especially given the potentially significant population consequences of sub-lethal effects. In the case of pesticides which are relatively non-toxic to mammals and birds, such as certain synthetic pyrethroids, errors made in extrapolations from hazard data are in general less likely to have such serious implications for terrestrial vertebrate wildlife, although risks of indirect effects may still be high.
The risk to wildlife of interactions between pesticides, or between pesticides and other chemicals, should also be considered. For example, a wide range of chemicals including certain pesticides are suspected of having endocrine disrupting effects and interactions between these are recognised as a key area requiring further research. Although field evidence for synergistic effects between pesticides or other chemicals is lacking, anticholinesterase effects are known to be potentiated by other classes of pesticide and the possible existence of such effects in the field involving OPs cannot be discounted.
There are recorded direct effects of pesticides on within-field populations of invertebrates and wild plants. Wider studies have shown longer term and larger scale declines in such groups although these have generally been less able to show an effect attributable to pesticides alone. Farmland holds a high proportion of Red Data Book plants, including such species as cornflower, red hemp-nettle, shepherd's needle and western ramping fumitory. Many of these are targets for priority action under the UK Biodiversity Action Plan, which cites herbicide use as among the factors associated with the decline in many instances. Although the major effect of herbicide usage in arable fields has been to reduce rather than eliminate weed populations, herbicides are considered to have made a significant contribution to the decline of the scarcer species.
Numerous studies have shown the short term adverse effects of broad spectrum insecticides on non-target organisms. Reductions of the order of 60-90% in populations of non-target invertebrates following applications of OP and pyrethroid insecticides have frequently been reported, often with reductions (of around 50%) in species diversity. These effects have often been short lived with recolonisation taking place within a few months but some projects (notably at Boxworth and the SCARAB project) have shown more prolonged effects on a range of invertebrate groups that inhabit arable fields.
The 20 year study of the effects of pesticide use in Sussex by the Game Conservancy Trust has shown over the period 1970-1995, a highly negative relationship between the use of organophosphate and pyrethroid insecticides and populations of a range of invertebrate groups (including spiders, beetles, bugs and butterflies). Use of pirimicarb showed no such negative effect, evidence of its selectivity to terrestrial arthropods compared with OPs and pyrethroids. Over this 20 year period, herbicide use within the Sussex study has shown little change with around 100% of the area treated since the early 1970s, although total spray area, due to intensification and multiple sprays, has increased twofold and the spectrum of susceptible weeds has similarly increased. Insecticide treatments showed an increase from <10% fields treated in the 1970s to 60-80% treated in the 1990s. Both the herbicide and insecticide usage data for Sussex are broadly consistent with national trends.
In such large scale studies, pesticides are usually only one of several factors which are associated with observed population declines. All major studies which have included a range of variables stress the role of crop type, rotation, field size, field margins, soil type, cultivation method - as well as pesticide use - in determining populations of non-target invertebrates. There is also considerable variability in the extent to which different species are affected by pesticide use.
The clearest evidence for the significance of pesticides in affecting population levels of such species comes from field scale trials in which pesticide input has been reduced. Recovery has been demonstrated in a range of groups where herbicide and insecticide use has been manipulated in conservation headlands. For example, higher densities of butterflies, beetles and other invertebrates and a greater abundance of broad leaved weeds have been recorded in selectively sprayed headlands which received no broad leaved herbicide or summer insecticide treatments.
Indirect effects of pesticides.
There has been growing interest in recent years over whether pesticides have been indirectly responsible for population changes in wildlife (particularly farmland birds) by reducing their food supply. Conclusive experimental evidence in the UK for the role of indirect effects of pesticides in the decline in bird numbers exists only for the grey partridge.
Widespread use of herbicides is considered to have contributed to the decline of the grey partridge since the 1960s through reducing availability of weeds for the invertebrate prey of gamebird chicks. Greater use of insecticides in cereals is likely to have further affected chick survival by reducing prey availability in the spring. Modelling of partridge populations shows that increased chick survival would result in population growth to a higher equilibrium level (although other factors such as density dependant shooting and predation will have a greater effect on population density). There is convincing evidence that both weed and arthropod prey densities increase in selectively sprayed field edges (conservation headlands) although the decline in spring cereals, ley farming and undersowing of cereals are also likely to have had important effects on partridge invertebrate prey. On average chick survival was 1.68 times higher in areas with reduced spraying than in fully sprayed headlands, and the number of pairs per km2 rose to almost double that prior to introduction of conservation headlands on one farm.
There are close associations between pesticide use and population decline of a further 11 farmland bird species, although other significant changes in agricultural practice (such as the change to greater winter cropping and loss of overwinter stubbles) may have played an equal or greater role.
Evidence for the change in diet of linnet suggests that previously preferred weed seed food items are now less available. A recent study of the corn bunting has shown that chick weight and survival is linked to invertebrate food availability, and that adult foraging for invertebrates is concentrated in areas having fewer pesticide applications. Overall, therefore, evidence is accumulating for the existence of mechanisms of indirect effects operating in other declining farmland bird species in a similar way to the grey partridge. It should be borne in mind that other factors are almost certainly operating so that manipulation of pesticide use alone is not necessarily the chief, or best, means of achieving any reversal. Several of these species are the subject of priority action under the UK Biodiversity Action Plan. Consideration of incentives for reduction or targeting of pesticide use have been incorporated as objectives into the action plans for grey partridge, skylark, linnet, cirl bunting, corn bunting, tree sparrow, turtle dove and bullfinch.
Pesticides in the Aquatic Environment
Toxicological and experimental field studies indicate that there are likely to be measurable adverse ecological effects of pesticides at concentrations found in some surface waters. The Environment Agency, the Scottish Environmental Protection Agency and the Environment & Heritage Service, DoE (NI) have been monitoring for a wide range of pesticides in Controlled Waters for a number of years and have published this information.
The Environment Agency data are derived from a number of different pesticide monitoring activities. This involves the collection of samples from over 3000 sampling sites in England and Wales each year and analysing for around 160 pesticides involving some 350,000 determinands. The significance of this information is assessed in a number of different ways which include comparison with:
Statutory Environmental Quality Standards (EQSs) - for compliance with the requirements of EC Directives such as the Dangerous Substances Directive (76/464/EC);
Non-statutory EQSs - which are generated by the Environment Agency for operational purposes including the setting of discharge consents;
the EC Drinking Water Directive Standard (0.1 µg/l for any pesticide) - which the Agency use also as an arbitrary standard against which to judge the quality of waters under their control.
There are in excess of 450 active substances approved for pesticide use and currently only a third of these are monitored. Further analytical method development is required, particularly for fungicides. Also monitoring has concentrated on older pesticides with very little done on newer substances such as the sulfonylureas and azole fungicides. Current results are, therefore, representative of an incomplete monitoring coverage (especially of groundwater) and, although incorporating most high usage pesticides, may be overlooking significant occurrences in water.
Summary results of monitoring from 1992-1996 show that the main EQS failures are for organophosphorus and synthetic pyrethroids used for ectoparasite control in sheep dips although certain herbicides have also shown occasional exceedences including isoproturon, diuron, 2,4-D and MCPA. Most exceedences of the 0.1µg/l limit are for agricultural and non-agricultural herbicides, of which isoproturon, mecoprop, diuron, MCPA and simazine are the most common. For some pesticides (particularly carbamate insecticides and synthetic pyrethroids) significant ecological effects have been detected at concentrations likely to arise from normal usage, giving rise to concern about other pesticides that have been less well studied in the field. Other effects including the toxicity of sediment bound pesticides and of pesticide additives, effects of breakdown products and of mixtures in the aquatic environment have received little attention. The Agency identified over 30 catchments in 1994 where changes in biota have occurred which may be linked to agricultural use of pesticides and other variables such as changes in sediment loading.
Sublethal effects of a range of pesticide groups on fish species as well as on marine invertebrates are also of concern. The severe and widespread population effects on dog whelks as a result of sublethal changes following exposure to organotin pesticides from marine antifoulants are well documented. Other in vitro effects on individuals of various species have included physiological changes arising from exposure to suspected endocrine disruptors (including insecticide groups such as organochlorines, pyrethroids and organophosphates and fungicides such as vinclozolin). The population implications of such effects if they occur in the field are unknown. Many of the examples recorded in the field have arisen from the effects of non-agricultural use of pesticides. However, the effects outlined above indicate that approved use of pesticides in agriculture, especially where this results in leaching or drift into headwater streams, is also a potential risk to populations of fish and aquatic invertebrates. Pesticide management may be as much an issue here as product choice. Measures which reduce drift or leaching into water courses (application technology, buffer zones) would need encouragement in order to reduce the risk of damage occurring to populations in the field.
Work is currently being carried out within the OECD to develop pesticide risk indicators for the aquatic environment which would enable trends in risk to be reported. A selection of indicators is being tested on UK usage data. Preliminary results do not encourage the view that the risk to the aquatic environment from the changing pattern and amounts of active ingredients used has decreased since the mid 1970s. Although this work is still at an early stage and may not yet have incorporated all factors which are relevant, the possibility exists that modern patterns of use are still presenting significant risks.
Pesticide misuse and abuse
The misuse of pesticides may be as a result of carelessness such as spillage, thoughtless disposal of waste, overspraying resulting in excessive dosing or spraying too close to wildlife areas or water bodies (disregarding buffer zones). Deliberate misuse, such as outdoor use of rodenticides in contravention of conditions specified on the label, has also been recorded. The most frequently recorded incidents in these categories involve seed and granular treatments and baits including molluscicides and rodenticides. In the case of seed treatments, primary exposure of the non-target species is likely to be the major source of poisoning.
The Wildlife Incident Investigation Scheme (WIIS) provides a major source of information about incidents (mainly mortality) arising from pesticide use or, predominantly, misuse as well as for other types of pesticide incident affecting certain groups of vertebrates and bees. Classes of chemicals most frequently involved in these incidents include the anti-cholinesterase carbamate and organophosphate insecticides, rodenticides and the molluscicides metaldehyde and methiocarb. Incidents involving other chemicals such as paraquat are occasionally reported but usually as a result of abuse. Whilst mostly the result of abuse or mis-use, these incidents provide some evidence for the potential sub-lethal or chronic impacts of certain classes of pesticides which may arise out of approved use. In some cases the risks posed to wildlife, evidenced from post-registration monitoring have led to necessary approval changes.
The deliberate poisoning of wildlife with pesticides has been implicated in the restriction of the distribution and spread of birds of prey such as the red kite and buzzard. Incidents involving birds such as the red kite, the subject of reintroduction programmes by the conservation agencies, are high profile and generate much concern. It is likely that the number of recorded incidents is significantly less than actual poisonings.
The misuse and abuse of pesticide products is illegal and enforcement action is taken against those responsible whenever possible. A pesticide tax is unlikely to play a significant role in dealing with these problems.
Summary
Pesticides play an important role in crop production to provide food for a growing world population.
Other farming activities are also known to have adverse effects on wildlife which are frequently difficult to separate from effects of pesticides.
The regulatory process for pesticides is designed to prevent products with unacceptable risks from reaching the market place. However, by definition, pesticides are hazardous chemicals and their lack of specificity towards target species places other animals and plants in the environment at risk from their use.
Pesticides can have an impact on non-target terrestrial species in a number of ways including direct effects of approved use, indirect effects of approved use, through contamination of water courses and groundwater, and as a result of misuse and deliberate abuse.
There is a need to remain vigilant with regard to monitoring effects of pesticides in areas concerning wildlife groups that are not currently monitored, and in looking at sublethal and long-term effects and interactive or synergistic effects.
There are recorded direct effects of approved pesticide use on field populations of invertebrates and wild plants including some species contained in the Red Data Book which are targeted under the UK Biodiversity Action Plan.
One 20 year study has shown significant effects of organophosphorus and pyrethroid insecticides on populations of a range of invertebrate groups. Bee mortality has frequently been caused by sprays of these two chemical groups.
Of particular concern are the indirect effects of pesticides on birds through reducing their food supply. There is conclusive evidence that reduction in populations of the grey partridge is due to effects of herbicides and insecticides on food supply. There are further probable associations of pesticide use with declines in populations of a further 11 species of farmland bird.
There are experimental studies that show there are likely to be measurable adverse ecological effects of pesticides found in water. It is likely that the occurrence of pesticides in water is greater than Environment Agency surveys reveal.
Most exceedences of Environmental Quality Standards for water are from the use of organophosphates and pyrethroids in sheep dips but they have also been recorded for certain herbicides. Exceedences of the EC Drinking Water Limit are mostly for herbicides.
Sublethal effects for a range of pesticide groups on fish species are also of concern as suspected endocrine disruptors. Approved use of pesticides, especially where this results in leaching or drift into headwater streams, is a potential risk to populations of fish and aquatic invertebrates.
Preliminary results from recently developed environmental risk indicators for the aquatic environment suggest that the risk of acute damage to aquatic organisms may not have reduced from the mid 1970s.
Pesticide misuse has given rise to a number of mortality incidents that are monitored through the Wildlife Incident Investigation Scheme (WIIS). These incidents provide evidence that certain classes of pesticides, notably organophosphorus and carbamate insecticides, do pose a risk to wildlife.
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Published 29 April 2000
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