Food chain and Bioaccumulation

Let us now analyze the ways in which environmental pollutants can reach the human organism through the food chain.

WHAT IS BIOACCUMULATION? By bioaccumulation we mean the accumulation of xenobiotics, including their lipophilic metabolites, which can be found in the food chain. These substances can be deposited in adipose tissue and in the central nervous system (CNS).

FOOD CHAIN, WHAT is it? For food chain we mean a passage of toxic substances from one food compartment to another, up to man.

Let's see an example to better understand the concept of the food chain.

A fish lives in the waters of a river polluted with toxic substances. These toxic substances contaminate the aquatic vegetation, consequently also the fish. The latter are caught and eaten by man.

All the substances accumulated in the meat of the fish are transferred inside the human organism, causing in many cases health problems. Within the food chain there may be a concentration of a lipophilic substance within a trophic species. Consequently, toxic concentrations increase as you get closer to the top of the food pyramid, as the larger fish accumulates the toxic from the smaller fish it feeds on. This amplification of a contaminant moving towards the higher levels of a trophic chain is called BIOMAGNIFICATION.

The xenobiotic can have different characteristics that make it more resistant to thermal degradation, easy to disperse, stable to electromagnetic radiation, not very soluble and resistant to biological and chemical degradation. Thanks to these characteristics the xenobiotic remains for a long time in the environment causing problems to the ecosystem.

The main xenobiotics are:

• Agropharmaceuticals;
• Medicines;
• Heavy metals (Lead, Mercury, Methylmercury, Cadmium);
• Synthetic chemicals (polychlorinated biphenyls or PCBs)
• Radionuclides.

Cadmium is a very dangerous heavy metal, as it has strong carcinogenic properties. It derives from a by-product of Zinc and Lead extraction, but it is also found in cigarettes, paints, plastics and marine waters. Since cadmium accumulates mainly in the kidneys, skeleton and lungs, its effects are serious damage to the DNA (it inhibits the processes of DNA correction, therefore it favors the development of neoplasms), to the renal system, to the system male reproductive system and the respiratory system. In the food chain cadmium is contained in abundance in mussels, oysters, clams and in all those molluscs that filter sea water.
In addition to cadmium, a very dangerous heavy metal is mercury (Hg), especially if methylated. Methylmercury is much more dangerous than elemental mercury because it has the characteristic of being more lipophilic, therefore easily absorbable by our body. Methylmercury causes severe damage to the neuronal system, particularly in growing (breastfeeding) children and the fetus. In the central nervous system, methylated mercury binds to the SH-groups of cytoskeletal proteins causing an "abnormal neuronal network, thus a deficit in nerve transmission.
Among the synthetic chemicals we find very dangerous compounds, which have as final target not man but the species of seabirds, the muria. The dangerous substances in question are polychlorinated biphenyls or PCBs. This environmental disaster has finally occurred of the 60s in Ireland, with the settlement of numerous industries. PCBs are organic compounds that can have a different degree of chlorination, as they can bind to more chlorine atoms. These compounds were used for industrial purposes because they were very heat stable and were not flammable. Over time it was realized that PCBs caused numerous problems in the liver and kidneys. To overcome this huge problem it was decided to abolish the production of these dangerous substances. However, the problem it was not resolved, because these substances had already accumulated in marine sediments, in aquatic vegetation, and consequently also in fish. those who ate the contaminated fish met with death. In fact, by taking fragments of liver and kidney tissue from dead birds, a very high concentration, up to 60,000 ppm, of PCBs was found.

If these xenobiotics through the food chain and come into contact with the pregnant human organism, the toxic substance passes to the fetus, causing serious health problems both to the mother, but especially to the fetus. After birth, the xenobiotic can be passed on by the nurse to the newborn through breastfeeding.

The effects that xenobiotics can have on infants depend on:

• dose;
• amount of xenobiotic;
• binding of xenobiotic to plasma proteins;
• molecular weight;
• solubility (the more the xenobiotic is fat-soluble, the more it passes into breast milk);
• degree of ionization;
• difference in pH between maternal blood - milk.

Other articles on "Food chain, Bioaccumulation, Biomagnification"

1. Toxicokinetics
2. Toxicity and toxicology
3. Biotransformation and xenobiotics