Antibiotics Resistance

Fish samples in Chennai test positive for formalin


Mains Paper 3: Environment | Conservation, environmental pollution and degradation, environmental impact assessment

From UPSC perspective, the following things are important:

Prelims level: Formalin

Mains level: Contamination of food items is a cause of concern.


Formalin – a carcinogen, traces in Fishes

  1. As many as 11 out of 30 samples of fish species purchased from two major fish markets in Chennai, on two different days, have tested positive for formalin, a cancer-inducing chemical used illegally to preserve fish.
  2. Both big and small lizardfish or Panna or kezhanga and paarai (Malabar trevally) were found to have formalin content of above 20 ppm (parts per million).
  3. Other varieties such as sura, octopus, eri vavvaal, ottu kanava, peikanava and kelithi had formalin of around 5 ppm.

Particulars of the Test

  1. For the test, a two-gram piece of meat from the fish was taken and put inside four ml of diluent and shaken so that the formalin will get into it.
  2. Then this diluent was poured into the bottle containing the reagent that turned yellow revealing that it had tested positive.
  3. It is a very sensitive reagent and can detect up to 0.5 milligram per kilo. The actual test takes only 10 minutes.
  4. Food Safety and Standards Authority of India (FSSAI) have been undertaking tests at fish markets and harbours across the State to test for formalin following a scare in neighbouring Kerala that fish sourced from here were chemically contaminated.

Why use Formalin?

  1. Usually, people who buy fish check the gills for freshness, if it is red it denotes freshness when formalin is used the gills remain red for longer periods.
  2. In some cases, fishermen also apply kumkum to retain redness.



  1. Formalin is 30-45% aqueous solution of Formaldehyde with water.
  2. Formaldehyde is a simple chemical compound made of hydrogen, oxygen and carbon.
  3. All life forms – bacteria, plants, fish, animals and humans – naturally produce formaldehyde as part of cell metabolism.
  4. Formaldehyde is perhaps best known for its preservative and anti-bacterial properties, but formaldehyde-based chemistry is used to make a wide range of value-added products.
  5. Formalin causes irritation in the eyes, throat, skin and stomach. In the long run, continued exposure causes harm to the kidneys, liver and can even cause cancers.
  6. In the fishing industry, formalin or formaldehyde is sprayed on the fish or injected into the fish or the fish is dipped into the solution. This helps keep the fish fresh for a longer time.
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