Iodine and Mercury Content in Raw, Boiled,

Overview

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Key numbers

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Analyzer (DMA-80). Thawing of the cod resulted on average in a 12% loss of iodine to the thawing
food composition databases (FCDB) and in food composition tables (FCT) (1). Changes in nutrient
and metabolism as it is active in the biosynthesis of thyroid hormones (10). At the same time, the range
purchased from Lerøy Seafood Group ASA (bought after tender). The cod weight ranged from 1–2.5 kg
was kept raw (n = 30). The other half was further prepared for three different cooking methods either
1: boiled (n = 10), 2: pan-fried (n = 10), or 3: oven-baked (n = 10). All cod fillets were weighted before
uncertainty 2810%cm),foranddrydisposable aluminum
and oven baking (n = 10)) were collected. Iodine was determined in all samples (n = 120) and mercury were weighed individually,
temperature pending analysis. In total, 60 samples of cod (raw (n = 30) and processed (n = 30)) and
and oven baking (n = 10)) were collected. Iodine was determined in all samples (n = 120) and mercury
was determined only in the cod fillet samples (n = 60), i.e., not in the liquid samples. To evaluate if the
Iodinethrough a 0.45 μm single use syringe and disposal filter. The 1% TMAH
solution contained tellurium (1 mg/L) which was used as an internal standard in order to correct for
and 50 μg/L) to measure the unknown iodine content in the samples. Iodine was determined by
filtered through a 0.45 µm single use syringe and disposal filter. The 1% TMAH solution contained
tellurium (1 mg/L) which was used as an internal standard in order to correct for instrument drift.
Samples were analyzed against a standard addition calibration curve (2, 5, 10, 20, and 50 µg/L)
The measurement uncertainty differs depending on the concentration range and is set to 15% for
iodine, receptively. The trueness for iodine in CRMs used in the present study (n = 6) was in good
1.5–1000 ng. For samples in this area the accuracy is 80–120%. Samples were weighed on a calibrated
used as CRM. A total of six samples of TORT-3 were placed at the beginning (n = 2), middle (n = 2),
and end (n = 2) of the analysis series to check the accuracy of the method throughout the analysis.
The CRM value for TORT-3 is 292 µg/kg for total mercury. Mean ± SD of analyzed CRM (n = 6) was
295 ± 11.4 µg/kg for total mercury, giving a mean accuracy of 101% (% relative SD: 3.9%). All results
were within the accepted area of the analyses (±20%). Mercury determination was performed in two
consecutive series and all analyzed values were above the LOQ of 0.08 ng mercury and the LOD
The iodine and mercury content in thawed raw cod (n = 30) (~100 g/piece of cod fillet) and iodine
in the associated thawing water are shown in Table 1, given as total µg per piece of cod fillets or in
samples with lower iodine content. The mercury content in the raw thawed cod ranged from 1.3 µg
(cod #19) to 6.3 µg (cod #13) per cod fillet wet weight with a mean ± SD and median mercury content
Table 1. Total iodine and mercury (µg) in raw cod fillets after thawing and iodine in thawing water
All (n = 30) 71.9 ± 86.7 8.5 ± 11.7 11.6 ± 3.4 2.6 ± 1.4
are reported in Table 2. The mean ± SD dry weight in the cod fillets (n = 30) was 19.1 ± 0.6% before
and 23.3 ± 2.0% after the different cooking methods. The dry weight increased significantly (p < 0.01),
All (n = 30) 19.1 ± 0.6 23.3 ± 2.0 101.3 ± 7.2 82.9 ± 7.2 18.2 ± 3.3
a mean ± SD weight of 101.3 ± 7.2 g. The weight decreased significantly (p < 0.01) in all fillets after
water reduced the iodine content per fillet with approximately 20%, but was not significant. The mean
30% loss of iodine to the boiling water. The iodine content given as per 100 g fillet was significantly
decreased by approximately 10%. Pan-frying and oven-baking did not cause any significant changes
iodine(μg/100 g) in cod fillets before and after the different cooking methods. Numbers are given as mean ± and
Table 3. Total iodine Iodine/Fillet,
(µg/100 g) in cod fillets before and after the different cooking methods. Numbers are given as mean

Methods (brief)

Spectrometry (ICP-MS) and mercury by atomic absorption spectrophotometry with Direct Mercury
Analyzer (DMA-80). Thawing of the cod resulted on average in a 12% loss of iodine to the thawing
Keywords: fish; cooking; processing; food composition data; analysis; ICP-MS; DMA-80;
2.2. Practical Procedure and Sample Preparation
and after processing. Figure 1 shows a schematic overview of the sample preparation of the cod fillets.
cod samples werefillet of approximately
samples pan-fried for 6–7 minutes
sub-sample rapeseed oil at
sample weretemperature.
separate plastic containers and frozen at minus 20 °C overnight. The samples were freeze-dried for
+25 °C,werewithalso collected
weight of the sample before and after freeze-drying. The method is validated, and measurement frying pan covered with Teflon
weight samples formrange
Freeze-dried samples were
analysis.all Incod samples
60 samples cod (raw (n (Labconco Freezone(n
samples liquidMI, USA)
The samples were homogenized, and a sub-sample of the wet sample

Implications

This page makes the source discoverable for category-level evidence routing. Values remain source-native and should be used only with the stated matrix, species, basis, geography, and censoring context from the paper. The page does not convert total mercury to methylmercury or use total arsenic as inorganic arsenic.

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised