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Environmental toxins: effect and origin

Environmental toxins, also referred to as xenobiotics, are chemicals that do not occur in biological substance cycles; they are difficult to degrade and often have a toxic effect. Xenobiotic substances are becoming an increasing problem because we are constantly exposed to them and because they slowly but surely poison us. The World Health Organisation (WHO) sees xenobiotic substances as factors that contribute, along with other factors, to the development of chronic diseases. In addition, they are regarded as the major causes for cancer, Alzheimer’s disease, autoimmune diseases, depression and type 2 diabetes. Although many xenobiotics have been banned, they continue to exert their effect, which is why they continue to be a focus of current research.

Moulds on fruit can produce dangerous mycotoxins. However, not all contaminations can be discerned with the naked eye. © Roger McLassus

Environmental toxins are also found in innovative construction materials or additives that are used to improve the environment of an individual's place of work or residence, e.g., wallpaper, varnish and paint. In addition, they are found in textiles such as carpets or clothing. These toxins are regarded as the major causes of what is known as "sick building syndrome" (SBS), in other words, human diseases resulting from poor indoor air quality due to improper exhaust ventilation or lack of fresh-air intake. Environmental toxins are also found in food (e.g., preservative agents, pesticides, drinking water), drugs (e.g., mercury in hypertension drugs). Numerous xenobiotics, including hexachlorbenzene used in plant protectants, lead to symptoms such as allergies, irritation of the airways and skin alterations. However, in many cases neither the origin of the toxic substances nor their effects have been scientifically investigated.

Acrylamide: cancer risk through food?

Ever since Swedish researchers discovered in 2002 that acrylamide is formed in food as a result of everyday cooking practices, academic and industrial researchers have sought to identify ways to reduce this. Acrylamide is a chemical substance whose risk potential had for a long time only been known in the plastics manufacturing industry. Animals develop cancer when exposed to acrylamide, which also leads to damage to the nervous system when administered in high doses. Reliable investigations on the doses that are harmful to human health (e.g. the effect of acrylamide on DNA) are still lacking, as are investigations on acrylamide contained in crispbread, biscuits and even coffee. Carcinogenic substances also occur in tobacco smoke, including formaldehyde, benzene and nitrosamines. The damaging effect of these substances is made worse through the presence of other tobacco smoke constituents such as acetaldehyde and ammoniac, which destroy the small hairs in the airways that normally clear foreign substances from the lungs. The length of time that tobacco particles remain in the respiratory system is thus prolonged and hence this also exacerbates the effect of carcinogenic substances.

After-effects despite ban of xenobiotics

Regulations limiting or banning the use of some known xenobiotics have been put in place, but the effects of substances such as asbestos will continue into the future. Asbestos is a silicate mineral that is resistant to fire, heat, electrical and chemical damage. Its fibrous composition and its resistance to biological degradation made it a popular material for use in electrical devices, machines and technical plants, brake pads and clutches, heating systems and it was also heavily used by builders and manufacturers. Contact with asbestos, for example the inhalation of asbestos fibres, can cause serious illnesses, including asbestosis, an occupational disease characterised by alveolar wall thickening. The connection between asbestos and the development of lung cancer and pleural mesothelioma has been scientifically recognised for several decades.

Particulate matter under the electron microscope: Microscopically fine particles can enter the human body, which is unable to defend itself against them. This leads to diseases of the respiratory or cardiovascular system. © Susanne Gauggel

Asbestos was banned in Germany in 1993 and in the EU in 2005. However, experts believe that people will continue to develop asbestos-related diseases in the future. Asbestos triggers chronic inflammation and leads to tissue scarring. The molecular mechanism that leads to the development of cancer is still not known in detail. Recent research results suggest that immunological processes that are triggered by the permanent exposure to asbestos fibres play a major role in the development of cancer. The risk of developing cancer is increased by other factors, including tobacco smoke. It will certainly take several decades before all the causes leading to potential asbestos-related health risks have been identified.

Influence on DNA and progeny

Current scientific investigations show that environmental toxins can lead to DNA modifications and affect sex chromosomes. Researchers from the University of Lund (Sweden) have shown that DDE (dichlorodiphenyldichloroethylene) and CB-153 (hexachlorobiophenyl), which accumulate as by-products during industrial and agricultural production processes, alter the number of X and Y chromosomes in sperm, which determine the sex of children. The human body reacts to different environmental effects by deactivating and secreting xenobiotics and other waste products that cannot be degraded. They are stored in the connective tissue, which sooner or later leads to dysregulation. However, the human body is able to compensate such dysregulations, at least to some extent. From a specific threshold level onwards, compensation is no longer possible, resulting in chronic ailments when the natural physiological processes are blocked.

Toxin mixtures with synergistic effects

The photo shows a monocyte that has absorbed particulate matter: many damaging processes with long incubation times occur in the body. © Susanne Gauggel

The effects of many xenobiotics are not known in detail, but it is known that the number of effects caused by xenobiotics is increasing. New toxic substances enter the environment and toxin mixtures play a prominent role. This is why these mixtures are at the centre of current research assessing the effect of environmental toxins. A researcher at the University of Konstanz is investigating ochratoxins (OTA and OTB), mycotoxins produced by mould fungi under suboptimal storage conditions (see article entitled "Invisible danger with long-term consequences"). Ochratoxins have been shown to have teratogenic, immunotoxic and carcinogenic effects, in particular in the kidneys. Preliminary studies have shown that ochratoxins display their toxic effects particularly strongly in combination with other mycotoxins. This piece of evidence is already taken into account in in vitro models used to identify the general risk potential of ochratoxins.

Michael Statnik - December 2010
© BIOPRO Baden-Württemberg GmbH

 

 

Glossary

  • Desoxyribonucleic acid (DNA) is a double-stranded, helical macromolecule encoding the genetic information of an organism.
  • Immunology is a scientific discipline dealing amongst others with the defence reactions of humans and animals against organisms such as bacteria, fungi, and viruses, but also with the defence reactions against foreign (non-self) cells and tissue or own (self) cells and tissue (autoimmune reactions).
  • Genetic sequences are successions of the bases adenine, thymine, guanine, and cytosine on the DNA (or uracil instead of thymine in the case of RNA).
  • The toxicity is the poisonousness of a substance.
  • Physiology is the study of the biochemical and physical processes in cells, tissues and organs of creatures.
  • Plasticity is the attribute of organisms to change their characteristic values under the influence of environmental factors. Therefore, neuroplasticity is the characteristic of neurons to change their response behaviour dependent from their activity. In most cases, the strength of the synaptic transmission is influenced (synaptic plasticity). The neuroplasticity or synaptic plasticity, respectively, is considered to be the basic mechanism in learning processes and in the formation of memories.
  • Alzheimer's disease (also called Morbus Alzheimer) is a slowly progressing dementia that manifests itself in an increasing reduction of brain functions. This disease mainly affects older people. It is primarily caused by intracellular deposits of a fragment of amyloid precursor protein (APP). This leads to a proceeding loss of neurons and therfore to a loss of brain mass. At the beginning of this disease, the concerned people only show a marginal obliviousness. In later stages, speech, the ability to reason and memory are mainly affected. In the end, the concerned people lose their entire sanity and personality.
  • Secretion is the release of a substance or fluid out of tissues or cells with or without glands.
  • Autoimmune diseases are diseases that are characterized by an immune system attacking the own body cells. This is caused by a failure of the immune system to discriminate between self and foreign cells or tissues.
  • Ethylene is a gaseous plant hormone. It is important for germination and senescence processes in plants such as ripeness of fruits, development of flowers, abscission of leaves in autumn and necrosis of plant parts. Ethylene is used in greenhouses to aerate fruits resulting in increasing maturation.
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