Is Leucomalachite Green in Food? A Look at Contamination & Safety

January 7, 2026 •

2 min read

While malachite green is an effective fungicide for fish, its metabolite, leucomalachite green, is the primary residue that accumulates in the fatty tissue of food-producing fish, raising significant health concerns. This chemical is not approved for use in food animals in many countries due to its potential toxicity. The presence of leucomalachite green in food is a matter of strict regulation and continuous monitoring.

Quick Summary

Leucomalachite green (LMG) is a toxic metabolite of the dye malachite green that can contaminate food, particularly fish from unauthorized aquaculture. Health risks include potential carcinogenicity, leading to bans on its use in food-producing animals by regulators globally. Ongoing monitoring detects and removes contaminated products from the market.

Key Points

Illegal Contaminant: Leucomalachite green (LMG) and malachite green (MG) are banned for use in food animals in many countries.
Primary Source is Aquaculture: Illegal use in fish and shellfish farming is the main source of LMG contamination.
Long-Lasting Residue: LMG is lipophilic and remains in fish fatty tissue, serving as a marker for illegal MG use.
Potential Carcinogen: LMG is considered a potential genotoxic and carcinogenic substance.
Advanced Detection Methods: Techniques like LC-MS/MS are used by regulators to detect LMG residues.
Risk Mitigation: Buying fish from reputable sources and supporting strong regulations helps minimize risk.

What is Leucomalachite Green and How Does It End Up in Food?

Leucomalachite green (LMG) is the reduced and colorless form of malachite green (MG), a synthetic dye. MG was historically used in aquaculture as a treatment for fish diseases, but it is metabolized by fish into LMG. LMG is lipophilic and accumulates in the fatty tissues of fish, persisting long after MG is gone. Regulatory agencies use LMG as a marker to detect the illegal use of malachite green in fish farming. Consumers can be exposed by eating contaminated fish or shellfish. While rare, deliberate adulteration of other food items with malachite green has also occurred.

Health Risks and Regulatory Actions

The prohibition of MG and LMG in food is due to health concerns. The JECFA has stated that an acceptable daily intake is inappropriate due to the potential genotoxic and carcinogenic nature of these compounds. Studies in animals suggest LMG could cause cancer, and the IARC classifies it as "possibly carcinogenic to humans" (Group 2B).

Regulatory bodies have strict policies:

Zero-Tolerance Policies: Many countries, including the USA, EU, UK, and Canada, have zero tolerance for MG and LMG residues in food from animals where their use is banned.
Reference Points for Action (RPA): EFSA has set an RPA of 0.5 µg/kg for the sum of MG and LMG in food of animal origin.
Monitoring Programs: Agencies like CFIA and FDA monitor and test food products for compliance.

Monitoring and Mitigating Risks

Advanced analytical chemistry techniques, such as LC-MS/MS, are used to detect MG and LMG residues at low levels. Rapid test strips are also available for quick screening.

Consumers can reduce exposure by choosing fish from reputable sources and regions with strong regulatory oversight. While trace levels have been found in wild fish, monitoring helps manage this. Deliberate misuse is the main concern, and strict enforcement aims to minimize it.

Comparing Malachite Green (MG) and Leucomalachite Green (LMG)


Feature	Malachite Green (MG)	Leucomalachite Green (LMG)
Form	Colored dye	Colorless metabolite
Persistence in Fish	Shorter residence time	Persists longer in fatty tissue
Solubility	Water-soluble	Lipophilic (fat-soluble)
Toxicity	Suspected mutagen, genotoxic	Suspected mutagen and genotoxic, possibly carcinogenic (Group 2B)
Marker Residue	Not the primary marker	Primary marker for illegal MG use

Detection Methods

Liquid Chromatography with Mass Spectrometry (LC-MS): Confirmatory analysis for MG and LMG.
Dual-Color Immunochromatographic Test Strips: Fast on-site screening tool.
QuEChERS Extraction: Sample preparation technique for quicker testing.

Conclusion

The presence of leucomalachite green in food is a concern stemming from its illegal use in aquaculture. However, stringent regulations and advanced testing methods in major food-producing regions aim to minimize consumer exposure. By sourcing fish from reputable suppliers who adhere to safety standards, consumers can effectively reduce their risk. The ongoing global effort in food safety continues to address the issue of contaminants like leucomalachite green. NCBI Source

Frequently Asked Questions

Leucomalachite green (LMG) is a colorless metabolite of malachite green (MG), a synthetic dye previously used in aquaculture.

LMG primarily enters the food supply through illegal use of malachite green in fish farming; fish metabolize MG into LMG, which accumulates in tissues.

No, in many countries, including the USA, Canada, and the EU, using malachite green on animals for human consumption is prohibited.

Animal studies suggest LMG may be genotoxic and carcinogenic, leading to its classification as possibly carcinogenic to humans by IARC.

Cooking methods like boiling or baking have limited effect on LMG levels, which is more stable than malachite green. Microwaving may offer some reduction but is not a reliable solution.

Food safety agencies use advanced analytical methods like LC-MS/MS to detect and measure LMG and MG residues at low concentrations.

While mainly linked to aquaculture, there have been rare reports of illegal food adulteration with malachite green in other items like sweets; however, this is not a widespread issue.

Choose fish and shellfish from reputable sources and retailers that follow international food safety standards. Supporting local, well-regulated producers is recommended.