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Transportation of nonindigenous species via soil on international aircraft passengers’ footwear


The potential for transported soil to harbour and spread nonindigenous species (NIS) is widely recognised and many National Plant Protection Organisations (NPPOs) restrict or prohibit its movement. However, surprisingly few studies have surveyed soil while it is in transit to provide direct support for its role in accidental introductions of NIS. Moreover, there are few border interception records for soil organisms because they are neither easily detected nor routinely isolated and identified. Better data would improve evaluations of risks from soil transported via different pathways, enable targeting of management resources at the riskiest pathways, and support development of new risk management methods. We surveyed organisms present in soil that had been removed from footwear being carried in the baggage of international aircraft passengers arriving in New Zealand and recorded high incidences, counts and diversities of viable bacteria, fungi, nematodes and seeds, as well as several live arthropods. These included taxa that have not been recorded in New Zealand and were therefore almost certainly nonindigenous to this country. In each gram of soil, there was an estimated 52–84% incidence of genera that contain species regulated by New Zealand’s NPPO, which suggests many were potentially harmful. 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. Comparisons with previously published data supported the hypothesis that survival of soil organisms is greater when they are transported in protected (e.g. in luggage) rather than unprotected environments (e.g. external surfaces of sea containers); this offers opportunities to develop methods for targeting management resources at the most hazardous soil pathways.

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We thank MAF staff who assisted with the study, particularly Rob Mulholland, Kevin Kennett, Merv Alexandra, Sandy Toy, Tamsin Smales, and Carolyn Whyte. Thanks also to Maria Minor (Massey University) for mite identification, Jo Berry (MAF) for assessing the status of mites found in samples, Diane Dahlkamp (AssureQuality Ltd, Palmerston North) for seed identification, Simon Bulman (Plant & Food Research, Lincoln) for nematode molecular identification, Maureen O’Callaghan (AgResearch, Lincoln) for advice on microbiological aspects of this study and Jerry Cooper (Landcare Research, Lincoln) for checking published and unpublished records from the New Zealand Organisms Register. John Kean (AgResearch, Lincoln), Victoria Allison (MAF) and two anonymous reviewers provided useful comments on earlier versions of the manuscript. This work was funded by New Zealand’s Foundation for Research, Science and Technology through contract CO2X0501, the Better Border Biosecurity (B3) programme.

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Correspondence to Mark McNeill.

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Mark McNeill and Craig Phillips contributed equally to the study.

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McNeill, M., Phillips, C., Young, S. et al. Transportation of nonindigenous species via soil on international aircraft passengers’ footwear. Biol Invasions 13, 2799–2815 (2011).

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  • Biological hazard
  • Invasion pathway
  • Invasive exotic species
  • Biosecurity
  • Pest risk analysis
  • Regulated item