Pesticide usage in Scotland: rodenticide use by local authorities 2015

Results and comparison with other surveys

Survey sample

All 32 local authorities ( LAs) in Scotland were contacted and asked to supply data relating to their rodenticide use during 2015. Twenty five LAs (78 per cent) supplied the information requested ( Figure 1). These LAs collectively represented 81 per cent of the Scottish population ( Table 4, Appendix 1).

In addition to collecting rodenticide use data, LA representatives were asked to respond to a series of supplementary questions. These questions related to their operatives' compliance with best practice in relation to rodenticide use, their use of non-chemical control methods and their experience of rodenticide resistance. Twenty nine LAs returned this data, representing 91 per cent of those contacted and 92 per cent of the Scottish population ( Figure 1, Table 4). The four LAs who returned the qualitative data but did not supply details of rodenticide use cited time constraints (either for them or their contracted pest control company) as the reason that data could not be provided.

Of the remaining three LAs, two did not respond to the survey and one could not participate as they do not offer a pest control service.

Figure 1 Scottish LAs supplying 2015 data

It should be noted that the information presented in this report only represents the data collected and, unlike previous UK surveys ⁽³⁾ , does not attempt to estimate total Scottish rodenticide use by LAs (refer to methodology section, Appendix 5). It should also be noted that LA use of rodenticides does not represent all rodenticide use in non-agricultural settings. Baiting in industrial, domestic and sewer settings which is not conducted by, or on behalf of, Scottish LAs is not captured by this survey.

Rodenticide use data

These data represent 25 LAs and 81 per cent of the Scottish population.

Rodenticide active substances encountered

Six active substances were used by the LAs providing data for this survey; brodifacoum, bromadiolone, coumatetralyl, difenacoum, difethialone and flocoumafen ( Table 1 & Figure 2).

All of the rodenticides encountered in this survey were anticoagulants, which prevent the synthesis of blood clotting factors and result in rodent death by haemorrhage. Five of the six compounds were second generation anticoagulant rodenticides ( SGARs), with bromadiolone accounting for 81 per cent of the active substance applied. Coumatetralyl was the only first generation anticoagulant rodenticide ( FGAR) reported.

Figure 2 Rodenticide active substances used by Scottish LAs in 2015 (percentage by weight)

The range of anticoagulant rodenticides reported in this survey are very similar to those encountered in recent Scottish agricultural surveys in which the rodenticides used are also almost exclusively SGARs with bromadiolone the principal active substance applied ^{(1)( 2)} . However, in contrast, non-anticoagulant compounds, such as alphachloralose and aluminium phosphide, are routinely encountered in agricultural rodenticides surveys, albeit at very low use levels.

Bromadiolone was also the most commonly used active substance in Scotland in the last UK local authority rodenticide use survey which was conducted in 2001 ³. However, a wider range of first generation active substances were also encountered in that survey, reflecting the differences in both rodenticide approval and resistance status at that time.

Quantity of rodenticidal products used

The LAs surveyed used ca. 14.9 tonnes of rodenticide products in 2015 ( Table 1). As active concentrations of these rodenticidal products are very low (0.0025 to 0.005 per cent of product weight), this equates to less than 1 kg of rodenticidal active substance. The remainder of the product is food bait which is used to attract rodents to consume the rodenticide.

The majority of products encountered contained a single active substance, with the exception of limited use (40 kg) of a product containing both bromadiolone and difenacoum ( Table 1, Figure 3).

The most commonly used products were those containing bromadiolone, accounting for ca. 12.5 tonnes of the rodenticide products applied (84 per cent of total use). In addition, ca. 1.6 tonnes of difenacoum containing products (11 per cent) and ca. 0.7 tonnes of brodifacoum products (5 per cent) were used. The remaining rodenticides (containing flocoumafen, difethialone, coumatetralyl and a difenacoum/bromadiolone mix) collectively accounted for 119 kg of rodenticide (less than one per cent of total use). More than 99 per cent of the rodenticidal products used were SGARs ( Table 1).

Figure 3 Rodenticide products used by Scottish LAs in 2015 (percentage by weight)

This pattern of rodenticide product use is very similar to that found in the most recent agricultural surveys where bromadiolone was also the most commonly used rodenticide (accounting for 77 and 58 per cent of use by weight on arable ⁽¹⁾ and grassland ⁽²⁾ farms respectively) with difenacoum and brodifacoum ranking second and third respectively. Bromadiolone, difenacoum and brodifacoum were also the three most commonly used rodenticides in the 2001 UK local authority survey ⁽³⁾ (accounting for 67, 17 and 9 per cent of total Scottish rodenticide use respectively).

Rodenticide use by setting

Survey respondents were asked to record, where possible, their rodenticide baiting activities in relation to the setting of use ( Table 2, Figure 4). All 25 of the LAs who responded to the survey conducted domestic baiting activities and the majority of rodenticide use was in domestic settings (ca.11.5 tonnes, 77 per cent). A further five per cent of rodenticides (ca. 0.7 tonnes) were recorded as being used in a combination of domestic and industrial settings and four per cent (ca. 0.5 tonnes) in solely industrial settings. Just under half of LAs (48 per cent) reported that they baited in industrial settings in 2015.

Very little use of sewer baiting was encountered in this survey. Only five of the LAs (20 per cent) reported sewer baiting activities with a total combined use of 34 kg.

Figure 4 Setting of rodenticide product use by LAs in 2015

During this survey, we asked about all rodenticide use by LAs. Six of the LAs surveyed conducted baiting on agricultural holdings on behalf of farmers. In this survey, this amounted to just over 2.2 tonnes of bait and 15 per cent of the total recorded use. Whilst this is recorded here for completeness in relation to LA baiting activities, it should be noted that agricultural baiting conducted by LAs is also included in the agricultural rodenticide surveys therefore caution should be exercised if compiling data from both LA and agricultural rodenticide reports to avoid double counting of LA baiting on farms.

Overall, the total LA baiting in non-agricultural settings was reported to be ca. 12.7 tonnes. It should be noted that this data represents only around 80 per cent of Scottish LAs and human population. This is an increase in comparison to total estimated Scottish non-agricultural use of rodenticides (10.9 tonnes) reported in the 2001 UK survey ⁽³⁾ . However, these data clearly indicate that the quantity of rodenticide used by LAs is considerably less than that reported in the most recent Scottish agricultural surveys of rodenticide use in arable and grassland sectors (113 ⁽¹⁾ and 217 ⁽²⁾ tonnes respectively).

Seasonal use of rodenticides

The season of rodenticide use was specified by all LAs returning rodenticide data. Overall, 99 per cent of baiting was reported to occur uniformly throughout the year, with very little rodenticide use being associated with a particular season (Figure 5). This baiting pattern represents multiple baiting operations as well as permanent baiting. This differs from reported use pattern on farms when greater use (approximately 60 per cent) occurs in autumn and winter, coinciding with the storage of harvested crops ⁽¹⁾⁽²⁾ .

Figure 5 Seasonal use of rodenticide products by LAs in 2015

Rodenticide bait type

Wax blocks were the most commonly used bait type in this survey, accounting for 64 per cent of all bait used (Figure 6). A further 35 per cent of the bait was grain. The remaining one per cent of rodenticides used consisted of a range of bait types including gel, pasta bait, grain based pellets and pastes, soft wax and foam. The use of foam as a delivery agent has not been previously encountered in Scottish rodenticide surveys.

The overall composition of the bait types encountered in this survey, are different from those reported in previous agricultural surveys where grain baits dominate and wax baits are far less frequently encountered, making up only around four per cent of total use ⁽¹⁾⁽²⁾ .

The type of bait selected is influenced by the setting of use. As LA baiting is primarily in domestic settings it may be advantageous to use wax blocks which are manufactured with a central hole to allow them to be secured within bait boxes. The use of wax blocks in bait stations reduces the likelihood of spillage and bait transference by rodents. This may be particularly important in domestic settings where exposure to domestic animals and householders, including children, must be prevented.

Figure 6 Type of rodenticide bait used by LAs in 2015

Target of rodenticide baiting

Survey respondents were asked to identify the target of their rodenticide use ( Figure 7). Where reason data were supplied the most common target was rats (59 per cent) followed by a combination of rats and mice (35 per cent). Only six per cent of use was targeted at mice alone.

These data are very similar to that reported in the 2014 arable rodenticide survey, in which it was reported that rats, rats/mice and mice were the target of 60, 38 and two per cent of rodenticide use respectively ⁽¹⁾ .

Figure 7 Target of rodenticide use by LAs in 2015

Supplementary data

These data represent 29 LAs and 92 per cent of the Scottish population.

Non-chemical rodent control

In addition to collecting data about rodenticide use, LAs were also asked whether they employed non-chemical methods of rodent control. Of those who responded, 22 LAs (76 per cent of the sample) stated that they adopted one or more non-chemical control methods. It was reported that alternative control was used to supplement use of rodenticides, or where there were concerns about rodenticide use in domestic settings, due to the presence of pets and children. They are also used in situations where rodenticides were ineffective (e.g. in cases of bait shyness where rodents have learned to associate food bait with discomfort and avoid rodenticides).

Of the methods reported, the most common was the use of break back traps, which were used by 21 LAs (72 per cent of the sample). Other methods of control encountered were live capture traps and glue boards (used by four and two LAs respectively). One LA reported using non-toxic monitor baits to assess pest presence prior to rodenticide use and another stated that rodent proofing and hygiene were improved to aid control of infestations.

Rodenticide resistance

Rodenticide resistance is known to occur in South West Scotland ⁽⁴⁾ and all respondents were asked if they had encountered, or were aware of, any rodenticide resistance issues in their LA areas.

Of the 29 who responded, the majority advised that they were not aware of any issues with rodenticide resistance (27 LAs, 93 per cent of responses). One LA, Dumfries & Galloway, which provided a negative response, stated that whilst studies have identified resistance in the west of the region they had not had any issues with control in practice. Two respondents did report known resistance in their LA area. Glasgow City stated that they were aware of difenacoum resistance in mice in some areas of Glasgow and resistance was also reported by South Lanarkshire (active substance not reported).

Compliance with best practice for rodenticide use

All local authorities were asked to complete a questionnaire in relation to their training history and their compliance with the principles of best practice for rodenticide use identified by the Campaign for Responsible Rodenticide Usage ( CRRU) ⁽⁵⁾ ( Table 3).

Of the LAs that responded, all stated that operatives had received training in rodenticide use. In relation to baiting, 100 per cent of LAs reported that they regularly inspect bait and always protect it from non-target animals. Ninety seven per cent of LAs stated that they always record the quantity and location of baits, 90 per cent search for rodent carcasses and 72 per cent remove bait after targeted baiting periods. The responses from LAs in relation to compliance with best practice are very similar to those provided by pest control professionals ( PCPs) who bait on agricultural farms ⁽¹⁾⁽²⁾ .

LAs were also asked how they disposed of rodent carcases. Of the 26 LAs that removed carcasses, the majority disposed of them at landfill sites (54 per cent). The remainder used a combination of disposal methods, including burial, incineration and use of waste disposal companies (Figure 8).

Figure 8 Rodent carcass disposal methods (no. of LAs)

Future rodenticide monitoring and stewardship

EU and UK Regulatory risk assessments have concluded that the use of anticoagulant rodenticides outdoors present a higher level of risk to non-target animals (such as predatory birds and mammals) than would normally be considered acceptable. However regulators recognise that, despite these risks, their use is necessary as part of a properly managed rodent control strategy. In order to be able to authorise these rodenticides UK Government must be assured that the risks to non-target animals are properly managed. This has been addressed by the introduction, in April 2016, of an industry led stewardship scheme managed by CRRU ⁽⁶⁾ .

Arable and grassland agricultural rodenticide surveys are conducted every two and four years respectively. As LA authority use of rodenticides is considerably less than that reported in agricultural settings, it is intended that this survey will be conducted every four years. This allows rodenticide use to be surveyed in a different use sector each year (arable, grass and fodder, arable and LA in 2016, 2017, 2018 and 2019 respectively). The data collected in this series of usage reports will reflect changes both in use pattern, resulting from changes to authorisation conditions, and in user training and compliance with the conditions of stewardship.

Whilst the LA data set does not capture all urban rodenticide use, its addition to the Scottish survey series may help to inform data on rodenticide residues in urban non-target species, as previous surveys have done in agricultural settings ⁽⁷⁾ .