Response to Comment on “Global Aquatic Sampling (AQUA-GAPS): Using Passive Samplers to Monitor POPs in the Waters of the World” We thank Bao and Zheng for their constructive comments (1) on our recent viewpoint article (2). Bao and Zheng suggest three additions and modifications to our proposed global passive sampling network for persistent organic pollutants (POPs) in the waters of the world (AQUAGAPS), namely, to (i) also monitor sediment porewater, (ii) include locations impacted by human activities, and (iii) protect passive samplers during deployments. Below, we discuss each point in detail.
1. Inclusion of sediment porewater as a monitoring medium There are several reasons why we deemed sediment porewater unsuitable for a global POPs monitoring program. First, the problems of contaminated sediments are almost always for local/ regional reasons, due to contamination by industrial and urban waste sources. This is really a task for national governments or regional programs involving neighboring countries, not global monitoring under the Stockholm Convention on POPs (SCPOP). Second, sediments are extremely heterogeneous on small spatial scales in terms of sedimentation rates, particle focusing, and contaminant concentrations, making it extremely difficult to establish reference sites in a contaminated estuary. Trends at any given site will mostly reflect on decision taken by local authorities/national governments, making it difficult to interpret for a global network. Lastly, sediments only play a sig-
nificant role in shallow environments, such as coasts and estuaries, while the water column arguably affects fish across most Lakes and Oceans. The purpose of the global monitoring approach at background sites is to measure the global response to actions taken to reduce POPs exposure.
2. Inclusion of locations impacted by human activities As we wrote in our viewpoint: We do not advocate including estuarine/harbor sites, as these reflect local or regional pollution events, privy to national or regional government action, but not the longrange transport of POPs addressed by the SCPOP. The unique feature of the SCPOP and the subject of much past research is the transport of POPs away from their place of production and use to remote and hitherto pristine sites. We thus think that while research into the presence of POPs at contaminated sites is important; this need not be done under SCPOP’s purview.
3. Protection of passive samplers using protective shields Contrary to Bao and Zheng’s claim, we did not advocate “naked deployments”, but wrote: While we have successfully deployed PE samplers without protection (e.g., 3-5), using stainless steel or copper casings will help guarantee retrieval of samplers and reduce biofouling. Field-testing of different deployment devices will help the community to find best solutions. We thus agree with their argument of protecting the samplers during long deployments. As far as performance reference compounds (PRCs) are concerned, it is true that their inclusion adds cost and analysis time. Yet to be able to unequivocally say that samplers reached equilibrium, they are es-
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sential components of passive sampling. As we noted in our article, for large molecular weight compounds, such as polybrominated diphenylethers, equilibrium might not be reached even during 2-month deployments. PRCs are the best way to assess the state of equilibrium and correct for nonequilibrium. RAINER LOHMANN* University of Rhode Island, Narragansett DEREK MUIR Environment Canada, Burlington, Ontario
[email protected]. (1) Bao, L.-J.; Zeng, E. Y. Comment on “Global aquatic passive sampling (AQUA-GAPS): Using passive samplers to monitor POPs in the waters of the world. Environ. Sci. Technol. 2010, DOI: 10.1021/es902379g. (2) Lohmann, R.; Muir, D. C. G. Global aquatic passive sampling (AQUAGAPS): Using passive samplers to monitor POPs in the waters of the world. Environ. Sci. Technol. 2010, 44 (3), 860–864. (3) Lohmann, R.; Burgess, R. M.; Cantwell, M. G.; Ryba, S. A.; MacFarlane, J. K.; Gschwend, P. M. Dependency of polychlorinated biphenyl and polycyclic aromatic hydrocarbon bioaccumulation in Mya arenaria on both water column and sediment bed chemical activities. Environ. Toxicol. Chem. 2004, 23 (11), 2551–2562. (4) Adams, R. G.; Lohmann, R.; Fernandez, L. A.; Macfarlane, J. K.; Gschwend, P. M. Polyethylene devices: Passive samplers for measuring dissolved hydrophobic organic compounds in aquatic environments. Environ. Sci. Technol. 2007, 41 (4), 1317–1323. (5) Morgan, E.; Lohmann, R. Detecting air-water and surface-deep water gradients of PCBs using polyethylene passive samplers. Environ. Sci. Technol. 2008, 7248–7253. Environmental Science & Technology edits all Letters for length, punctuation, and clarification of references. Authors approve of changes prior to publication.
ES101053M
10.1021/es101053m
2010 American Chemical Society
Published on Web 05/10/2010
