Toward standardization of sample collection and preservation for the quality of results in biomonitoring with trees – A critical review
Tarricone, Kathrin; Wagner, Gerhard; Klein, Roland
Ecological Indicators 57 (2015), 341-359; available online 26 May 2015
Tree leaves and needles are commonly used in biomonitoring as reliable indicators of environmental pollution to monitor a wide range of mainly airborne contaminants such as heavy metals and persistent organic pollutants (POPs). The most severe challenges are the reproducibility and comparability of results. This is the only basis upon which correct assessment can be ensured. Standardizing the collection and preservation of leaf samples can overcome such problems and improve the quality of the results. On this account, efforts are being made to promote standardization on national (Association of German Engineers, VDI) and international (European Committee for Standardization, CEN) level. The objective of this review is to investigate the current state of quality assurance in passive biomonitoring by analyzing 86 peer-reviewed papers on tree leaf-sampling and use. We show that little attention has been given to standardizing how leaves are collected in the field and stored as well as to the documentation of selection criteria and sampling conditions. Important information is often absent, including crucial aspects of sample collection and preservation, for example, the selection of sampling sites, exposure, sampling period, age and condition of target compartments. Potential standards are suggested and discussed as a foundation for the development of quality assurance standards to conceptualize and perform sampling. For some aspects of sampling the current literature yields little information to derive and establish standards. In the first place, this concerns the selection of sample species. Besides of this, it is important to document and report data concerning sampling conditions in a publication. Overall, further research is urgently required to define scientifically valid standards, which will ensure a high level of quality and comparability of the samples collected in the field.