Abstract
Introduction. Fish can sometimes be contaminated with several highly toxic substances at once, e.g. heavy metals, pesticides, and preservatives. In this regard, it is essential to determine the presence of these harmful chemicals in fish products. The research objective was to analyze the level of organochlorine pesticide residues and other toxic substances in Tenualosa ilisha L.
 Study objects and methods. The study featured organochlorine pesticide residues and other toxic substances in raw and cooked samples of fresh and salted T. ilisha, which is a popular dish in Northeast India, especially in the state of Tripura. The analysis involved tests for formaldehyde, pesticides, and heavy metals. Formaldehyde content was estimated using high-performance liquid chromatography, pesticides content – by low-pressure gas chromatography/tandem mass spectrometry, and heavy metals – by inductively coupled plasma/mass spectrometry.
 Results and discussion. The salted samples had a high content of formaldehyde, though it remained within the normal range. Both fresh and salted samples demonstrated high concentrations of heavy metals such as zinc, copper, and selenium. The salted sample appeared to have a high content of toxic organochlorine pesticide residues. Frying and boiling of fresh and salted fish decreased formaldehyde and organochlorine pesticide residue contents but did not reduce heavy metal content.
 Conclusion. T. ilisha was found to be quite safe for human health.
Highlights
Fish can sometimes be contaminated with several highly toxic substances at once, e.g. heavy metals, pesticides, and preservatives
The salted samples had a high content of formaldehyde, though it remained within the normal range
Formaldehyde, which is often used as an antimicrobial preservative, is considered to be carcinogenic to humans, which was confirmed by the International Agency for Research on Cancer (IARC) [6, 7]
Summary
Fish is a highly nutritive part of human diet. First of all, it is the primary source of polyunsaturated fatty acids (PUFA), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The normal range of formaldehyde is 2–50 mg/kg, and the maximum can reach 60 mg/kg in fruits and marine fish [8] Heavy metals, such as lead, chromium, mercury, arsenic, etc., are well-known contaminating chemicals that cause water and soil pollution [12]. The objective of the present experiment was to analyze the level of organochlorine pesticide residues and other toxic materials in raw and cooked samples of fresh and salted T. ilisha. After adding 5 mL of acetonitrile, the samples were sonicated for 30 min at 25–30°C and shaken for 30 min in a shaking water bath at 150 rpm at room temperature. A standard pesticide mix, 500 ng/mL in 0.05% formic acid in methyl cyanide, was used for 5 and 1 ng/g spiking levels in the recovery experiments. A one-way analysis of variance (ANOVA) was performed to determine a 5% level of significance
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