title: Is it appropriate to composite fish samples for mercury trend monitoring and consumption advisories?
abstract: Monitoring mercury levels in fish can be costly because variation by space, time, and fish type/size needs to be captured. Here, we explored if compositing fish samples to decrease analytical costs would reduce the effectiveness of the monitoring objectives. Six compositing methods were evaluated by applying them to an existing extensive dataset, and examining their performance in reproducing the fish consumption advisories and temporal trends. The methods resulted in varying amount (average 34-72%) of reductions in samples, but all (except one) reproduced advisories very well (96-97% of the advisories did not change or were one category more restrictive compared to analysis of individual samples). Similarly, the methods performed reasonably well in recreating temporal trends, especially when longer-term and frequent measurements were considered. The results indicate that compositing samples within 5cm fish size bins or retaining the largest/smallest individuals and compositing in-between samples in batches of 5 with decreasing fish size would be the best approaches. Based on the literature, the findings from this study are applicable to fillet, muscle plug and whole fish mercury monitoring studies. The compositing methods may also be suitable for monitoring Persistent Organic Pollutants (POPs) in fish. Overall, compositing fish samples for mercury monitoring could result in a substantial savings (approximately 60% of the analytical cost) and should be considered in fish mercury monitoring, especially in long-term programs or when study cost is a concern.
authors.affiliation: University of Toronto, Toronto, ON M1C 1A4, Canada.
authors.forename: Nilima
authors.initials: N
authors.lastname: Gandhi
authors.affiliation: University of Toronto, Toronto, ON M1C 1A4, Canada; Ontario Ministry of the Environment and Climate Change, Toronto, ON M9P 3V6, Canada; University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada. Electronic address: s.bhavsar@utoronto.ca.
authors.forename: Satyendra P
authors.initials: SP
authors.lastname: Bhavsar
authors.affiliation: University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Gewurtz
authors.affiliation: University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
authors.forename: Ken G
authors.initials: KG
authors.lastname: Drouillard
authors.affiliation: University of Toronto, Toronto, ON M1C 1A4, Canada.
authors.forename: George B
authors.initials: GB
authors.lastname: Arhonditsis
authors.affiliation: Ontario Ministry of the Environment and Climate Change, Toronto, ON M9P 3V6, Canada.
authors.forename: Steve
authors.initials: S
authors.lastname: Petro
mesh_terms: D000818:Animals; D004784:Environmental Monitoring / Q000379:methods*; D005399:Fishes; D005506:Food Contamination / Q000032:analysis*; D008628:Mercury / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Advisories; Compositing/pooling; Fish; Mercury Hg; Monitoring; Sensitive population