Onion as a mean of testing the toxicity of environmental pollutants

Environmental pollution has a very broad impact on humans, animals, plants and other living things. Many pollutants have an effect on human health. Pollutants can be synthetic or natural materials. Industrial waste can contain heavy metals that pollute water and soil, while the agricultural sector can cause insecticide residues in soil and irrigation water.

Pollutant toxicity testing is usually carried out using experimental animals because this test assumes that animals are more sensitive than plants to chemical effects. In addition, animals have a similar system to humans, so that they have good validity when applied to humans. There are several obstacles in using animals as toxicity bioassays, for example it takes a long time and is expensive. The toxicity of a substance can be observed through chromosomal damage caused by a compound. Observation of chromosomes in plants can be done easily and does not require sophisticated tools, so plants are a good alternative as bioassays.

Onion root is a research material that has been widely used in the analysis of the toxicity of a pollutant. Onion bulbs are easy to obtain and can be grown easily. Roots are part of plants that are very useful in toxicity testing, because they are the first part to be exposed to contaminants in the soil or in water. The onion root meristem contains a high proportion of mitotic cells which are very important in chromosome observation. Onion chromosomes are large, making it easier to observe.

It is also very easy to make chromosome preparations from the tip of the onion roots. Onions are rooted by soaking in water, after the roots grow, they are transferred to a pollutant solution for a certain period of time. Then the root tips are cut and immersed in a fixative consisting of acetic acid and alcohol. After that, the root tips were soaked in hydrochloric acid to soften the roots. The root tip was placed on a slide then stained with aceto-orcein and covered with a cover slip, and then pressed with the thumb so that the cells spread. Chromosomal damage is then observed under a microscope.

Some types of chromosome damage that are often observed in onions are fragmented chromosomes, sticky chromosomes and chromosome bridges during anaphase and telophase. Several studies have shown that onions are effective in detecting toxicity. Therefore the toxicity test using the onion system is an important test tool in environmental monitoring.