Pesticide usage in Scotland: Rodenticide use by Local Authorities 2023

Data and Methodology

There are 32 local authorities in Scotland (Table 6, Figure 10). Each LA was sent an e-mail survey designed to collect information about their use of rodenticides in 2023 in relation to season, setting and target of use. The survey also included questions about compliance with best practice in relation to rodenticide use, use of non-chemical control methods and experience of rodenticide resistance.

Prior to the start of the survey an attempt was made to establish a named contact at each LA to whom the survey could be sent. In some cases this was the same person who had responded to the 2015 survey, or a new person identified via telephone call or e-mail to the council. With a number of councils it was difficult to make contact or enquiries went unanswered. Once this was done, an initial introductory letter and survey form was sent to each LA by e-mail to the named contact where possible, or to an enquiries e-mail for the Environmental Health team. These were followed by a reminder e-mail, ten weeks after survey initiation, if data had not been received. In some cases further follow-up telephone calls were required to elicit a response or for data clarification.

Both previous agricultural rodenticide surveys^{(2, 3)}, and the UK local authority survey conducted by CSL in 2001⁽⁴⁾ estimated total rodenticide use statistically based on the sample data collected. The agricultural reports are based on data from a random stratified sample of agricultural holdings and total agricultural use is estimated by ratio raising (comparing data from the sample of farms with the total population within each stratum reported in the June agricultural census). The 2001 UK local authority report data were raised within counties/metropolitan districts by a factor accounting for the human population represented by nil returns, to give an estimate of national rodenticide use. The UK survey received returns from 51% of LAs, accounting for 53% of the UK population.

In contrast to the above rodenticide surveys, in this report the data have been collated and presented as a sample rather than using ratio raising to produce a statistical estimate of total use. When the 2015 Local Authority survey⁽¹⁾ was analysed there was no correlation between human population or population density with rodenticide use, either in relation to Scotland as a whole or within geographical regions. This was discussed with a BIOSS statistician and the decision was taken that the most appropriate action to avoid mis-estimation was to present the data as a sample. This survey has taken the same approach. As the sample covers 84% of LAs representing 91% of the Scottish population it is considered to provide a robust overview of how rodenticides are used by Scottish LAs. Each LA operates different levels of rodent control, with some only undertaking or arranging it (via contractor) on their own properties and perhaps for social housing tenants, some LAs also offer a service to private domestic housing, while some others offer a full commercial service to both domestic and industrial customers. The level of rodenticide use in each LA is likely to be heavily influenced by these differences, and it may explain why no correlation was previously found with population.

The dataset underwent several validation processes as follows; (i) checking for any obvious errors upon data receipt (ii) checking and identifying inconsistencies with use and approval conditions once entered into the database (iii) 100% checking of data held in the database against the raw data. Where inconsistencies or a lack of clarity relating to products were found these were checked against the records and with the LA if necessary. Due to rounding, there may be slight differences in totals both within and between tables. Additional quality assurance is provided by sending reports for independent review. In addition, the Wildlife Management Unit and Scottish pesticide survey unit are accredited to ISO 9001:2015. All survey related processes are documented in Standard Operating Procedures (SOPs) and our output is audited against these SOPs by internal auditors annually and by external auditors every three years.

These surveys may be subject to measurement bias as they are reliant on respondents recording or reporting data accurately. As this survey is not compulsory it may also be subject to non-response bias, as some LAs could be more likely to respond to the survey than others.

Figure 10 Scottish LA boundaries

Map shows the boundaries and locations of all surveyed LAs in Scotland. An inset box provides a close up of LAs across central Scotland.