# Aflatoxin M1

Aflatoxin M$_1$ is a chemical compound of the aflatoxin class, a group of mycotoxins produced by three species of Aspergillus – Aspergillus flavus, Aspergillus parasiticus, and the rare Aspergillus nomius – which contaminate plant and plant products.
Aspergillus flavus produces only B-type aflatoxins. Aflatoxin M$_1$ is the hydroxylated metabolite of aflatoxin B$_1$ and can be found in milk or milk products obtained from livestock that have ingested contaminated feed. The carcinogenic potency of aflatoxin M$_1$ in sensitive species is about one order of magnitude less than that of aflatoxin B$_1$. Aflatoxin M$_1$ is usually considered to be a detoxication by-product of aflatoxin B$_1$. The main sources of aflatoxins in feeds are peanut, meal, maize and cottonseed meal.

## Chemical structure

The chemical structure of aflatoxin M$_1$. Aflatoxin M$_1$ is the 4-hydroxy derivative of aflatoxin B$_1$ and is secreted in the milk of mammals that consume aflatoxin B$_1$. Aflatoxin M$_1$ has a relative molecular mass of 328 Da and has the molecular formula C$_{17}$H$_{12}$O$_7$.

## Sources of exposure

Aflatoxin M$_1$ may be found in milk, including human milk. In cows, sheep, goats and buffaloes that have consumed feeds contaminated with aflatoxin B$_1$, aflatoxin M$_1$ will be formed as a result of the metabolic process in the livers of ruminants and excreted in their milk. Humans can be exposed to the toxins through consumption of contaminated milk and other foods.

## Pathology

The effect of aflatoxin M$_1$ was much weaker than aflatoxin B$_1$ in producing liver cancer. The limited animal studies carried out to determine toxicity of aflatoxin M$_1$. Aflatoxin M$_1$ has toxic and carcinogenic properties. The toxicity of aflatoxin M$_1$ in ducklings and rats seems to be slightly less than that of aflatoxin B$_1$. The carcinogenicity is probably one to two orders of magnitude less than that of the highly carcinogenic aflatoxin B$_1$.

## Bioconversion pathway

Aflatoxin M$_1$ (AFM1), the principal hydroxylated metabolite of AFB1, is found in the milk (hence the designation M) of mammals fed with contaminated feedstuff. Carry-over of aflatoxin B$_1$ (AFB1) as AFM1 in the milk of dairy cows has been established to range from 0.3% to 6.2%. However, AFM1 was also found in lactating mothers' milk. Several studies reported carcinogenic and immunosuppressive effects similar to that of AFB1, on both humans and other animals, even if with a less potent effect. However, AFM1 is the only mycotoxin for which maximum residue limits (MRLs) in milk were established.

## Toxicological study

Several studies have been undertaken of the toxic effects of aflatoxin M$_1$ in laboratory animals. However, in comparison to aflatoxin B$_1$, relatively little is known about the toxicity of aflatoxin M$_1$, primarily because of the difficulty in obtaining sufficient quantities of the pure compound necessary for extensive toxicity testing.
| Species | Sex | Dose | Result |
| Trout (fry) up to 12 months | Male | 8 μg/kg 4-64 μg/kg (120 treated/group) 800 μg/kg | No tumours (0/110) Liver tumour response: 0.086 % 50 % tumours at 9 months |
| Fischer rats | Male | 0 μg/kg 0.5 μg/kg 5 μg/kg 50 μg/kg | Liver cancer 0 % neoplastic nodules 0 % Liver cancer 0 % neoplastic nodules 0 % Liver cancer 0 % neoplastic nodules 0 % Liver cancer 5 % neoplastic nodules 16 % |
| Fischer rats | Male | 1 mg/rat | Liver cancer 1 of 29 |

## Genotoxicity

The potency of aflatoxin B$_1$ and aflatoxin M$_1$ in inducing DNA damage and genotoxicity was tested in Drosophila melanogaster. Aflatoxin M$_1$ was found to be a DNA-damaging agent, with an activity about one-third that of aflatoxin B$_1$.

## Analytical methods

Many methods have become available for the determination of aflatoxin M$_1$ in milk. In particular, solid-phase correction and immunoaffinity chromatography cartridges offer good possibilities for efficient clean up. Both thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC) are adequate techniques to separate and determine aflatoxin M$_1$ in extracts of milk. Enzyme-linked immune sorbent assay (ELISA) is more popular, due to ease of use and properties which are conducive to rapid screening and semi-quantitative determination. Aflatoxins determinations are usually expensive and employ environmentally unfriendly procedures, thus, the search for new materials and technologies, that are both ecologically safe and inexpensive its rice husk as an adsorbent method.

## Regulation

According to a recent review conducted by the Dutch National Institute for Public Health and the Environment (RIVM) on behalf of the Food and Agriculture Organization (FAO) approximately 60 countries have set specific limits for aflatoxin M$_1$. The European Union countries generally apply a maximum level of 0.05 μg/kg milk. Some countries in Africa, Asia and Latin America also propose this level. In contrast, the USA as well as some European and several Asian countries accept a maximum level of 0.5 μg/kg aflatoxin M$_1$ in milk, which is also the harmonized Mercosur limit applied in Latin America. The 0.5 μg/kg limit for aflatoxin M$_1$. Thus, the maximum permitted level of aflatoxin M$_1$ in milk in the EU is among the lowest in the world, and is based on the ALARA (As Low As Reasonably Achievable) principle. Considering the carry-over into milk and the established adverse effects on animal health, approximately 45 countries have set specific levels for aflatoxin B$_1$ in feed for dairy animals. To support compliance with the maximum levels in milk intended for human consumption, stringent maximum levels were also set in the EU for feed stuffs which might be consumed by dairy cows. A limit of 0.005 mg/kg feed for dairy cattle is applied in the EU countries and in the new member states as well as in Europe Union countries, but only in few countries outside Europe. This level is below the no-effect level in target animals.