Determination of Toxins in Animal-Derived Foods: Testing Scope, Analytical Methods, and Applications

Toxin determination in animal-derived foods is a critical food safety control that protects consumers from naturally occurring hazards such as marine biotoxins, histamine, tetrodotoxin, and feed-derived mycotoxins in shellfish, fish, milk, meat, and eggs. Accredited third-party laboratories apply validated LC-MS/MS, HPLC, and immunoassay methods in accordance with ISO, AOAC, EN, and GB standards to quantify these toxins at or below regulatory limits. This article summarizes the sample types, testing items, analytical techniques, quality assurance requirements, and practical applications of toxin testing for animal-origin food products.

Technical Overview

Animal-derived foods, including fish, shellfish, crustaceans, milk, dairy products, meat, eggs, and honey, can contain naturally occurring toxins that originate from the animal's diet and environment or from microbial activity during handling and storage. The most significant groups are marine biotoxins accumulated by filter-feeding bivalve molluscs during harmful algal blooms (HABs), biogenic amines such as histamine formed during spoilage of scombroid fish, marine neurotoxins such as tetrodotoxin and ciguatoxin, and mycotoxins such as aflatoxin M1 and ochratoxin A that carry over from contaminated animal feed into milk, meat, and eggs.

Most of these toxins are heat-stable and are not destroyed by cooking, processing, or preservation; therefore, laboratory determination is the primary, and often the only, effective control measure. Acute intoxications such as paralytic shellfish poisoning, diarrhetic shellfish poisoning, scombroid poisoning, and ciguatera can develop rapidly after consumption, while chronic exposure to aflatoxin M1 is associated with hepatocarcinogenic risk. Quantitative toxin testing is consequently embedded in food safety legislation worldwide, including the Chinese national standards GB 2761 and GB 2762, the EU hygiene and contaminant regulations, and Codex Alimentarius standards.

Methodology has evolved significantly over the past two decades: the traditional mouse bioassay has largely been replaced by instrumental liquid chromatography-tandem mass spectrometry (LC-MS/MS), which allows multi-analyte quantification of numerous toxin congeners in a single extraction and run. This shift has improved sensitivity, specificity, animal welfare, and comparability of results across accredited third-party laboratories operating under ISO/IEC 17025 quality systems.

Testing Samples

Shellfish and Other Bivalve Molluscs

Mussels, oysters, clams, cockles, and scallops are the principal vectors of marine phycotoxins because they filter large volumes of water and retain toxin-producing microalgae. Depending on the standard applied, the whole edible tissue or the whole body minus shell is homogenized and analyzed for both lipophilic and hydrophilic toxin groups.

Finfish and Crustaceans

Scombroid species such as tuna, mackerel, bonito, and mahi-mahi are tested for histamine; pufferfish (fugu) products are tested for tetrodotoxin; and large predatory reef fish such as grouper, snapper, and barracuda are screened for ciguatoxins. Shrimp, crab, and lobster may also be included in biotoxin surveillance programs in certain jurisdictions.

Milk and Dairy Products

Raw milk, UHT milk, milk powder, cheese, yogurt, and infant formula are analyzed for aflatoxin M1, the hydroxylated metabolite of aflatoxin B1 excreted by dairy cows consuming contaminated feed, and, where relevant, for ochratoxin A and other feed-related mycotoxin markers.

Meat, Eggs, and Derived Products

Pork, poultry, eggs, and processed products such as sausages and dry-cured meats can carry over ochratoxin A and other mycotoxins from cereals used in animal feed, while certain fermented or cured products additionally require histamine and biogenic amine control.

Testing Items

The testing scope is organized by toxin group, each with defined maximum limits in official regulations:

• Paralytic shellfish poisoning (PSP) toxins: saxitoxin (STX) and analogues including neosaxitoxin, gonyautoxins, C-toxins, and decarbamoyl toxins; typical limit 800 µg STX diHCl equivalents per kg of shellfish flesh.
• Diarrhetic shellfish poisoning (DSP) toxins: okadaic acid (OA), dinophysistoxins (DTX1 and DTX2) and their esters; typical limit 160 µg OA equivalents per kg.
• Azaspiracid (AZP) toxins: AZA-1 to AZA-3 and analogues; typical limit 160 µg AZA equivalents per kg.
• Yessotoxins (YTX) group; typical limit 3.75 mg YTX equivalents per kg.
• Pectenotoxins (PTX); regulated together with the OA group in the EU at 160 µg per kg.
• Amnesic shellfish poisoning (ASP) toxin: domoic acid and epi-domoic acid; limit 20 mg per kg.
• Neurotoxic shellfish poisoning (NSP) toxins: brevetoxins (BTX-2 and BTX-3), regulated primarily in the United States shellfish program.
• Tetrodotoxin (TTX) in pufferfish and, increasingly, in bivalve monitoring programs; non-licensed pufferfish products must be free of detectable toxin in many markets.
• Ciguatoxins (CTX), including Pacific, Caribbean, and Indian Ocean congeners, in reef fish.
• Histamine and other biogenic amines: histamine, putrescine, cadaverine, tyramine, and spermidine; EU limits of 100 to 200 mg per kg (up to 400 mg per kg for enzyme-matured products of certain species).
• Aflatoxin M1: 0.05 µg per kg for milk and dairy in the EU (0.025 µg per kg for infant formula) and 0.5 µg per kg under Codex and GB 2761 for milk.
• Ochratoxin A and other carry-over mycotoxins in animal tissues, eggs, and processed meats.

Testing Methods

Sample Preparation

Edible tissues are homogenized, and toxins are extracted with aqueous methanol for hydrophilic toxins such as PSP toxins and domoic acid, 80 to 100 percent methanol for lipophilic toxins, acidified organic solvents for mycotoxins, or hot acidified water for tetrodotoxin. Cleanup steps may include liquid-liquid partitioning, solid-phase extraction (SPE), alkaline hydrolysis of toxin esters for total DSP determination, pre- or post-chromatographic oxidation for PSP fluorescence detection, and immunoaffinity column (IAC) purification for aflatoxin M1 and ochratoxin A.

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

LC-MS/MS is the reference technique for regulated marine biotoxins and mycotoxins because it separates, identifies, and quantifies dozens of analogues in a single run using matrix-matched calibration and isotope-labeled internal standards. The EU-harmonized LC-MS/MS protocol, recognized under Commission Regulation (EU) No 15/2011, covers the OA/DTX, AZA, YTX, and PTX groups, and EN 16204 describes the corresponding procedure for lipophilic algal toxins in shellfish. AOAC Official Method 2011.02 and equivalent GB 5009 methods determine the full PSP toxin profile by LC-MS/MS, and multiple-reaction-monitoring (MRM) acquisition provides the sensitivity required for aflatoxin M1 at sub-µg/kg levels and tetrodotoxin at low µg/kg levels.

HPLC with Fluorescence or UV Detection

HPLC-FLD combined with immunoaffinity cleanup remains a workhorse for aflatoxin M1 in milk and dairy products (ISO 14501 / ISO-IDF 171; GB 5009.24). PSP toxins can be determined by LC-FLD after prechromatographic oxidation (AOAC 2005.06), domoic acid by HPLC-UV or diode-array detection (AOAC 991.26), okadaic acid group toxins by HPLC-FLD after derivatization (EN 14133), and histamine by ion-exchange or reversed-phase HPLC after dansyl or benzoyl derivatization, as well as by fluorometry (AOAC 977.13).

Immunochemical and Rapid Screening Methods

ELISA kits (for example, AOAC Official Method 2006.02 for okadaic acid) and lateral-flow immunochromatographic strips enable high-throughput, on-site screening of raw materials, live-tank shellfish, and landing-site lots. Positive or legally relevant results are confirmed by LC-MS/MS, because immunoassays may cross-react differently with individual analogues and report group-equivalent concentrations rather than congener-specific data.

Bioassays and Emerging Techniques

The mouse bioassay (AOAC 959.08) was the historical official method for PSP and DSP screening but is being phased out for ethical and specificity reasons. Functional assays such as receptor-binding assays and neuroblastoma (Neuro-2a) cytotoxicity tests remain valuable for ciguatoxin screening, where calibration standards are scarce, and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) is increasingly used for non-targeted toxin screening and congener discovery.

Quality Assurance

Accredited third-party laboratories validate methods for selectivity, linearity, limit of detection, limit of quantification, recovery, repeatability, reproducibility, and measurement uncertainty, and verify ongoing performance through certified reference materials (CRMs), proficiency testing, and matrix-fortified controls under an ISO/IEC 17025 quality management system. Toxicity equivalence factors (TEFs) published by scientific expert bodies are applied to convert individual congener concentrations into group-equivalent results for direct comparison with regulatory limits.

Applications

• Regulatory compliance testing and official control programs for domestic and imported animal-origin foods.
• Biotoxin monitoring of shellfish harvesting areas and classification or reopening of production zones after harmful algal blooms.
• Lot release testing and certificate-of-analysis generation for seafood processors, exporters, and retailers.
• Feed-to-food carry-over studies for aflatoxin M1 and ochratoxin A along the dairy and livestock supply chain.
• Epidemiological investigation of foodborne poisoning incidents and post-marketing surveillance.
• Support for product development, shelf-life and cold-chain verification, and HACCP validation for histamine control in scombroid fish handling.

FAQ

What sample size and shipping conditions are required?

Typical requirements are 200 to 500 g of homogenizable edible tissue per sample, shipped frozen or chilled with ice packs and accompanied by full chain-of-custody documentation. For shellfish, the laboratory usually removes the shell and homogenizes the whole edible tissue before extraction.

How long does toxin testing take?

Immunoassay or lateral-flow screening results are typically available within one to three working days, while confirmatory LC-MS/MS or HPLC-FLD testing generally requires five to ten working days depending on the toxin scope and the need for hydrolysis, derivatization, or re-extraction.

Are these toxins destroyed by cooking?

No. Most marine biotoxins, tetrodotoxin, histamine, and aflatoxin M1 are heat-stable, so conventional cooking, canning, drying, or freezing cannot reliably render a contaminated product safe. Prevention through testing and source control is the only effective mitigation.

How should a laboratory choose between screening and confirmatory methods?

Screening methods are suitable for internal quality control and rapid triage of large sample batches, whereas regulatory reporting, lot release for export, and dispute resolution require confirmatory chromatographic methods, preferably LC-MS/MS, with full validation data and accreditation.

How are multi-congener results compared with legal limits?

Individual congener concentrations measured by LC-MS/MS are multiplied by toxicity equivalence factors and summed to obtain a group-equivalent value, which is then compared directly with the maximum limit, for example 800 µg STX equivalents per kg for PSP toxins.

How frequently should shellfish be monitored?

Monitoring frequency is risk-based: weekly or biweekly sampling is common during harmful algal bloom seasons or in historically affected harvesting areas, with intensified sampling triggered by elevated phytoplankton cell counts or toxin findings until two consecutive compliant results are obtained.