Methylmercury determination in freshwater biota

Overview

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Key numbers

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of certiﬁed reference materials. For biota, mean recovery was 100 ± 2% and relative standard deviation (RSD)
≤ 6.8% for method I, and mean recovery was 98 ± 7% and RSD ≤13% for method II. For sediments, recovery of
Limits of detection (LOD) were 0.7 μg kg−1 and 6 μg kg−1 , respectively. Both techniques were tested for MeHg
analysis in freshwater invertebrates, ﬁsh and sediments, covering a large range of MeHg values (1.9–670 μg kg−1
• Passing-Bablock regression revealed a slight disproportion between methods, with line slope = 1.058 (95%
Me200 Hg) and 216 and 245 (Me201 Hg) (Table 1, Spreadsheet 1). Due to the isotopic pattern of
tetraethylborate 97% from Sigma-Aldrich (Darmstadt, Germany).
made with methanol and hydrochloric acid 18% with a proportion of 30/70% v/v. An internal standard
5.49 ± 0.04 μg g−1 , 96.5 %, ISC Science, Oviedo, Asturias, Spain) in 99 mL of ultrapure water 1% HCl.
NaBEt4 1% was obtained by dissolving 100 mg of sodium tetraethylborate 97% in 10 mL of ultrapure
water. Calibration standard solutions was prepared in the range 0.03–2 μg MeHg and a six-point
acid 1 M) and 3 mL of 1 M KOH to reach a pH value of 5.5. For ethylation, 1 mL of NaBEt4 1% was
limit (LOD) is 0.01 ng Hg, the working range is 0.05 to 600 ng Hg.
L-cysteine solution (1%) was obtained by mixing 12.5 g of sodium acetate anhydrous, 1 g of L-
(10 0 0 mg Hg L−1 , Scharlab S.L., Barcelona, Spain) with potassium dichromate 1 % and hydrochloric
solutions prepared by dilution of the 500 μg Hg L−1 stock solution with the L-cysteine solution (1%).
concentration of mercury into the extract (μg Hg L−1 ), 6 is the volume of L-cysteine solution (1%)
as mean absorbance of the L-cysteine solution (1%) + 3 times the standard deviation and LOQ as
LOD was 0.7 μg kg−1 and LOQ 1.4 μg kg−1 of MeHg (Table 2). For method II, resulting LOD was 6 μg
were analyzed (Table 2).
ranged between 90.8 and 103.4%, while average RDS was 8.4%.
with a mean recovery of 94.5% (RSD = 8.8%) and 67.7 ± 6.4 μg MeHg kg−1 for method II (the
Values of MeHg (μg kg−1 ) in biological and sediment certiﬁed reference materials (mean ± standard deviation) obtained with methods I and II. n = number of analyses, R = mean percent
MeHg μg kg n. MeHg μg kg R% RSD % n. MeHg μg kg−1 R% RSD %
GC chromatogram showed no other organomercury forms in the sample), with a recovery of 90.3%
Both methods were evaluated for analysis of biological samples collected in the ﬁeld (Table 3).
Sediment samples were successfully analysed in GC-MS over a range of 1.9–26 μg MeHg kg−1 .
Average RDS was 7.5%. As expected for freshwater sediments (23,25,26), MeHg concentrations
represented ≤ 1.5% of total Hg (Table 3). For this reason, most sediment analyses carried out with
AMA-254 (using 0.2 g d.w. of the sediment sample) resulted as < LOD (Table 2).
littoral” (26 μg kg−1 MeHg according to method I analysis, Table 2): 0.4 g, 0.6 g and 0.8 d.w.. However,
certiﬁed materials and natural samples (n = 20). Spearman’s rank correlation coeﬃcient was
absence of a systematic error, the 95% conﬁdence intervals must include 0 for the intercept and 1 for
bias is -7.36% (95% CI: -11.6 to -3.0%), and the agreement interval falls between -25.7 and 11.0%
relative standard deviation, THg = total mercury (n = 3), N.D. = not determined, i.e., the method failed determining MeHg in the sample (see text for explanations).
Lake Maggiore, Pallanza Basin Pallanza sublittoral, 2013 4 6.1 ± 0.7 10.7 4 <LOD - 3207 ± 13
Lake Maggiore, Pallanza Basin South of Isola Bella, 2013 4 6.8 ± 0.1 2.2 4 <LOD - 6276 ± 167
//ec.europa.eu/jrc/sites/default/ﬁles/Full%20JRC%20Tecnical%20report%20SOP.pdf.

Methods (brief)

compared to direct mercury analyzer
after microwave acid digestion and aqueous phase NaBEt4 ethylation; II) Automated Mercury Analyzer, after
Limits of detection (LOD) were 0.7 μg kg−1 and 6 μg kg−1 , respectively. Both techniques were tested for MeHg
Method name: Methylmercury in freshwater biota and sediments by GC-MS or automatic mercury analyzer
biota and sediment samples, using two different analytical systems: I) static headspace and gas
chromatography with single quadrupole mass spectrometry detection, and II) Automated Mercury
sample digestion was preferred, also because in the literature it is considered as more suitable for
extraction to limit the extraction of matrix interferences, and thus to decrease the LOD. To optimize
the literature. The direct mercury analyzer is used here also for determination of total mercury (THg)
in samples according to US-EPA (14).
Sample collection and pretreatment
The performance of both methods was tested by analyzing samples of biota and sediments
collected in Lake Maggiore basin (Northern Italy). The ecological quality of the lake and its main
Swiss Waters (CIPAIS) (www.cipais.org) (15,16). Fish and sediments collected in the western part of
the lake (Pallanza Basin) and benthic invertebrates (insects, crustaceans) and sediments collected
mercury cell chlor-alkali plant located along the Toce River (17–19). Moreover, ﬁsh collected in another
Sample volume (mL) 20
analyzed. All samples were freeze-dried before analysis. Biological tissues were homogenized with

Implications

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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