I'm wondering if some of you are aware of existing conversion factors for levels of metallic contamination in fish muscle tissues. In the present work, I'm focusing on metallic contamination, so not currently interested in lipid content of the tissues.
Depending of the contexts, concentrations are expressed relatively to fresh or dry weight. By example, working on muscle sample is more convenient when dried, but concentrations are expressed relatively to wet weigh in European directives, requiring conversion factors.
In most of the paper I read, concentrations are expressed relatively to wet or dry weight, and are then converted using a 5 times conversion ratio. But no information about the actual measurement of the ratio is provided, and I feel this value is largely empirical.
So, is someone aware of the rationale for this value ? Are you aware of papers specifically investigating this point ?
Thanks
Dear Pierre,
I guess you could use this factor of 5 times if you can support this by publications. Otherwise it might be easier to calculate your own ratio. Have some fresh muscle, weight it, dry it and weight it again. Actually, I always measure the ratio wet/dry by myself before measuring the contamination concentration in my plant tissue.
Best regards
Thanks Geoffrey. My question was maybe not correctly formulated :This 5 ratio is largely used in several papers (including mine) to convert concentrations. But I could not find out what is the calculation behind this value.
So, I'm currently doing the protocol you described in a large dataset of fish to check the effet of several variables on this value but I would like to find the origin of this 5 ratio. And finally, I would like to know if people has their own conversion factors, or if they always measure wet and dry weigh of their sample.
Fat soluble contaminants have been often expressed on a fat basis rather than on a dry weight or product basis. This does require only fat extraction and no further determination of dry weight or fat content of the sample.
Kees,
The question was amended based on your answer.
I feel the lipid content is not of prime interest since I work on metallic contaminant, that are not the most lipophilic compounds.
In addition, the aim of this study is to determine accurate conversion factors to compare values measured in dried muscle with values provided by regulation agencies like European Union.
Thanks for the supplementary information. From my personal experience, I never used the "factor 5 ratio", I did always calculate mine. All scientists in my lab are doing the same, and I have seen that several time in literature. So I do not know where come from this factor 5. Especially as human body is suppose to have 75% of water, so it will be a factor 4. Another myth ready to be busted.
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