After the tragic gas leakage industrial accident that occurred in LG polymers chemical plant in Visakhapatnam. Thousands of people were affected by the styrene gas leaked from the industry. Total 11 deaths were reported till May 9 2020. This is not the first time when humans are exposed to such hazardous chemical substance. There are several research journals in which researchers have published the after-effects of styrene exposure to human and in this report, we are going to understand briefly what happens when you are exposed to styrene.

What is STYRENE?

Styrene is a colourless to yellowish oily liquid(a derivative of benzene), also known as vinylbenzene. On exposure to air or light styrene undergoes polymerization and oxidation as it has a reactive vinyl group which polymerizes at a significant rate at room temperature, but more rapidly at elevated temperature. Styrene is used widely in manufacturing reinforced plastics, rubber, andresins. The majority of commercial styrene production is done by dehydrogenation of ethylbenzene.

preparation of styrene by dehydrogenation of ethyl benzene
Fig: preparation of styrene by dehydrogenation of ethyl benzene

Styrene metabolism in humans 

When occupational exposure to styrene occurs mainly via inhalation, it is converted to styrene oxide by the cytochromeP-450 monooxygenase system(enzymes) primarily found in liver. Although liver has the highest activity ,kidney,lung,intestine,and skin also metabolize styrene and styrene oxide

Styrene oxide is considered to be the major primary metabolite of styrene in mammals.It can undergo several detoxification reactions i.e it may hydrolyze to styrene glycol or conjugate with glutathione.This lead to formation of main metabolic end products, mandelic and phenyl- glyoxylic acid found in urine of exposed humans.

Health impact of styrene

Acute Toxicity

The adverse effects of a substance shown in a short period are known as acute toxicity. The two major effects of acute exposure to styrene in humans include irritation (both skin and respiratory tract) and central nervous system (CNS).

Symptoms are as follows:

  • Irritation of the eyes, nose, skin.
  • Nausea, headache, listlessness, muscular weakness, and unsteadiness.
  • Ciliastasis (loss of movement of cilia in the trachea)

Though the reason underlying this impact is not known very well some researchers have pointed that the sensory irritation occurred by the reaction of styrene (or metabolites) is because it reacts with the sulfhydryl groups on the free afferent trigeminal nerve endings located at the surface of the nasal mucosa. 

Chronic Toxicity

The adverse effects of a substance shown in a long period of time is known as a chronic toxicity. There have been several reports of the carcinogenicity(causing cancer) of styrene and styrene oxide. It was observed by some researchers that styrene and styrene oxide shows mutagenic( causes a change in DNA of a cell) characteristics in both bacterial and mammalian systems.

1. Genetic toxicity

It is a type of toxicity in which the genes or the nucleotides of the DNA gets damaged or altered. Styrene requires metabolic activation like active metabolite styrene oxide to produce genotoxic effects. Active metabolites produce effects only when a sufficient amount of epoxide is formed and is available for DNA reactions. Styrene and styrene oxide was able to induce-

  • DNA breaks: It is a type of DNA damage in which the phosphate backbone of the DNA strands is broken. When the DNA is repaired by our body sometimes this creates an alteration of the DNA which lead to mutation.
  • Point mutation: It is a type of mutation where a single nucleotide base is inserted or deleted which lead to a point mutation

2. Cytogenetic toxicity

It is a type of toxicity which alter the chromosome structure and disruption in the process of cell division. The first report on a cytogenetic investigation on workers exposed to styrene in a boat factory was published by Meretoja and coworkers (1977). Since then, several similar studies have been published, many of them showing increased cytogenetic effects in exposed person. Styrene was shown to induce cytogenetic effects such as-

  • Chromosomal aberrations (CA): When one chromosome is missing or extra in human it is known as aneuploidy and lead to chromosomal aberration. The normal human chromosome no is 46 referred to as 2N.N,3N are example os chromosomal aberration.
  • Sister Chromatid Exchange reduction: SCE is the exchange of genetic material between two identical sister chromatids. This is done to form new recombination and pass it to the offspring. The decrease in induction of SCE was observed in cells exposed to styrene. The possible reason may be that the styrene oxide increases unscheduled DNA synthesis and DNA repair leading to cell death.
  • Micronuclei formation: As styrene exposure cause chromosome fragments and when it is not able to incorporate into daughter cell nuclei during cell division it leads to the formation of micronuclei.

Conclusion:

Thus, styrene and its active metabolites not only have a short term impact but also long term impact on human health so industrial safety should be kept in mind so that we are not exposed to such hazardous

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