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Consequences of using pooled versus individual samples for designing environmental monitoring sampling strategies
Swedish Museum of Natural History, Sweden.
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Swedish Museum of Natural History, Sweden.
Swedish Museum of Natural History, Sweden.
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2014 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 94, 177-182 p.Article in journal (Refereed) Published
Abstract [en]

Choosing an appropriate sampling strategy for chemical analysis within environmental monitoring includes the important decision of whether to sample and store individual or pooled samples. This choice impacts on future analyses from Environmental Specimen Bank samples. A number of advantages exist to support using either individual or pooled samples for temporal trend studies. However, it is important to know the total and analytical variance to be able to design the best sampling strategy. Statistical power in temporal or spatial studies is determined by the random/unexplained sample variation. The relationship between chemical analytical error and other sources of variation, as well as the cost for collection, preparation of samples and chemical analysis, will determine the number of individuals in each pool, and the number of pools that should be analysed to achieve high cost efficiency and good statistical power. Various scenarios of different numbers of individual samples, different numbers of pooled samples containing various numbers of individual specimens, the relationships between chemical analytical error and other sources of sample variance, have been compared by simulating random sampling from computer generated populations using realistic measures of variation from ongoing monitoring activities. These results offer guidance in the design of a cost-efficient, statistically sound sampling strategy.

Place, publisher, year, edition, pages
2014. Vol. 94, 177-182 p.
Keyword [en]
Analytical error, Biological variation, Environmental monitoring, Pooled samples, Specimen banking, Statistical power
National Category
Chemical Sciences Earth and Related Environmental Sciences
Research subject
Environmental Chemistry
Identifiers
URN: urn:nbn:se:su:diva-98263DOI: 10.1016/j.chemosphere.2013.09.096ISI: 000327685300025OAI: oai:DiVA.org:su-98263DiVA: diva2:686148
Note

AuthorCount:5;

Available from: 2014-01-10 Created: 2014-01-03 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Improved Assessment in Environmental Monitoring of POPs: Using monitoring data from the aquatic ecosystem and human milk
Open this publication in new window or tab >>Improved Assessment in Environmental Monitoring of POPs: Using monitoring data from the aquatic ecosystem and human milk
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis deals with several aspects of monitoring of persistent organic contaminants (POPs) in biological matrices, for example choice of sample, sampling design, and statistical treatment of data both for temporal and spatial trends and for compliance towards a set target value. The efficiency has been evaluated through statistical power analyses. Contaminant data from more than 4 decades from the Swedish National Monitoring Programs for monitoring of contaminants in biota (marine, freshwater and human health), has been quantitatively evaluated both temporally and spatially and for compliance. The aim was also to evaluate the suitability of different matrices, i.e. herring (Clupea harengus), guillemot (Uria aalge) egg, cod (Gadus morhua), perch (Perca fluviatilis), eelpout (Zoarces viviparous), blue mussel (Mytilus edulis), pike (Esox lucius), Arctic char (Salvelinus alpinus) and human milk, for monitoring of POPs with the overall aim to improve the assessment within monitoring programs.

The results show that variation can be reduced by using pooled samples including more specimens but fewer chemical analyses, which in turn generate a higher statistical power to a lower cost, at least in cases where the cost of collection and sampling is considerably lower than the cost of chemical analysis. However, there are also a number of advantages using individual samples, such as information of sample variance and maximum value, which allows the choice of an appropriate central measure and direct adjustment of confounding factors.

Generally, the levels of polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs) and hexachlorobenzene (HCB) have decreased both in marine and freshwater biota but concentrations are still higher in the Baltic compared to e.g. the North Sea. The levels of dioxinlike-PCBs and polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) have decreased in human milk over time, but not to the same extent in fish and guillemot egg from the Baltic and the freshwater environment. This may be explained by the dietary advice developed by the Swedish Food Administration with the goal that girls, reproductive aged, and pregnant women should eat less food containing high levels of PCDD/Fs. Thus the levels in milk could continue to decrease at the same rate although the temporal trend in the environment has slowed down or leveled out.

The most essential regarding the choice of species and matrices for contaminant monitoring, is that the species and organ fit the purpose of the monitoring.

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry, Stockholm University, 2016. 83 p.
Keyword
Environmental monitoring, temporal trends, power analysis, sampling strategy, PCBs, DDTs, HCHs, HCB, PCDD/Fs, fish, bird eggs, blue mussels, human milk
National Category
Other Chemistry Topics
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-134769 (URN)978-91-7649-527-8 (ISBN)978-91-7649-528-5 (ISBN)
Public defence
2016-12-09, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 14:00 (English)
Opponent
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Available from: 2016-11-16 Created: 2016-10-18 Last updated: 2016-11-16Bibliographically approved

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