To help answer these questions, Better Border Biosecurity (B3) funded a research project led by Mark McNeill and involving AgResearch and Plant and Food researchers including Craig Phillips, Lee Aalders, Sandra Young and Farhat Shah. The study was initiated after discussions with Ministry of Agriculture and Fisheries (MAF), including MAF staff at Christchurch airport, and began by looking at soil on footwear. To carry out the study, two of the B3 team travelled to either Auckland or Christchurch international airports and, with the cooperation of MAF staff, collected soil from the soles of contaminated footwear declared by arriving passengers to MAF.

The study found that on average every pair of shoes carried by international air passengers is contaminated with about one gram of soil. The small amount of soil on shoes presented an interesting question because as McNeill observed, “The wisdom from microbiologists and nematologists was that we were not going to find much in such small samples. In fact, we found a much greater number and diversity of organisms than anyone expected.”

On average, each gram of soil removed from passengers’ shoes contained 2.5 seeds, 41 nematodes and high counts of both bacteria and fungi, including plant pathogenic species. Between 52% and 84% of genera recovered from contaminated footwear contained potentially harmful species regulated by MAF.

Variation in the incidences and counts of soil organisms with sample weight, footwear type and season at the port of departure indicated it may be possible to develop methods for targeting management resources at the riskiest footwear.

The other component of the project was to investigate which cleaning methods are most effective, and again the results have been quite surprising. MAF’s standard procedure had involved dipping footwear in a solution of the disinfectant VirkonTM followed by scrubbing. However, this research offers the view that while Virkon is still needed in special cases (for example, where footwear has been in contact with livestock or contaminated surfaces and where animal viruses might be suspected), in most cases scrubbing shoes with water is adequate to remove most potential invaders.

These results also have implications for MAF, the Department of Conservation (DOC) and regional authorities when managing the movement of visitors through ecologically sensitive areas or quarantine zones. For example, McNeill points out that not a lot is known about the effectiveness of footwear washing bays and what improvements can be made to help reduce the spread of potentially unwanted organisms into economically or ecologically important areas.

The research also found preliminary evidence that soil on sea containers contains fewer viable organisms than soil on shoes, perhaps because it is more exposed to harsh environmental conditions during transit. As a result, the team has now shifted its focus to sea containers to evaluate whether this is really true. By comparing different pathways and defining which ones are riskiest, the project will help MAF to decide where they should invest their limited resources to get “the most biosecurity bang for their buck”.

Results from this most recent work should be available in May 2012, but preliminary data suggests that the container soil does indeed contain fewer nematodes and seeds per gram of soil compared to soil found on footwear. Conversely, the container soil may contain species of parasitic nematodes not found on footwear.

McNeill says, “This has been a good team project that has pulled in microbiologists, nematologists, plant ecologists and others to deliver some very important results for end users.”

Further down the track, potential research avenues include evaluating the risks that foreign species transported in soil could establish given suitable hosts and habitats, and comparing these exposure risks between the various importation pathways.