In our last blog we explored different methods of testing emissions - chemical and biological. Biological methods begin with defining an endpoint for exposure and using systems that are best suited to understand whether exposure has occurred or not.
Biological tests can be conducted at different levels - single cell, small animals, humans and at community level. In this blog we'll explain what are the strengths and weaknesses of these biological methods.
Testing Impact for single cells
These are very useful to understand how much exposure is needed for a response to appear. Since only a small number of cells are needed, a large number of experiments can be conducted in a very short span of time. The flip side of such test results is that when cells don’t respond, it cannot be taken as safe exposure. This is because it is quite possible that the levels needed to bring about a response could be very high. The tester then has to evaluate whether such high levels are likely to be reached in real life situations or not.
Testing impact on small animals
These tests help understand a coherent response of a living being to the exposure. The animal chosen for the study must be similar in its response to humans. This often varies based on the type of disease, e.g. cancer related response could be similar but immune system related responses can be very different in animals so may not give a true picture of effects on humans. Nevertheless, these test bridge the gaps where it is not possible to test the effects of the pollutant on all the cell types individually.
Testing impact on normal or diseased humans
Studies in normal and diseased persons are also conducted to understand the effects of exposure. These studies are conducted by exposing healthy individuals to specific doses of pollutants in a preprogrammed way and observing whether a health condition, say respiratory distress, develops or not. Since this is not how real-life exposure happens, some experts label these test settings as artificial. Nevertheless, these tests are useful to monitor clearly defined health outcomes.
In diseased individuals also, the effect of exposure to pollutants can be checked. But there is an additional problem of delinking disease effects from pollutant effects. In other words, is the person showing the hazard because s/he is already sick or is the pollutant making the condition worse?
Testing impact on large communities or populations
The study of exposure in large communities that live near incinerator plants is probably the most holistic way to understand whether there are effects of exposure. These are called epidemiological studies and are the best view into long-term, low-dose exposure. Even here doubts remain if the effects are truly because of exposure or due to natural differences amongst people. Since these effects are seen in human beings as a whole, there is no way to understand the threshold dose at which the effects might have started to appear. An evaluation of responses seen with cellular tests may be needed to give clues about the threshold dose.
Overall, even though biological testing methods can investigate the effect of exposure to a pollutant at various levels of life, a combined look at all the data is needed by experts to unambiguously label an emitted compound as low-risk.
Reference for content : https://www.sciencedirect.com/book/9780123736154/fundamentals-of-air-pollution
The blog is by Sowmya Raghavan (Member SWMRT) , Support by Divya Tiwari (Member SWMRT)