Acclimatization to pollution, adaptation, resistance and tolerance in ecotoxicology

Acclimation, adaptation, resistance or tolerance can be defined as the capacity of organisms to cope with stress, either natural changes in temperature, salinity, dissolved oxygen and toxins or chemicals depending on anthropogenic sources.

Defense mechanisms: physiological responses to chemical stress (biomarkers)

• Types of biological response:
• Changes at the molecular level (genetic integrity, biochemical responses)
• Changes at the physiological or organ level (histopathological disturbances, immunotoxicological changes)
• Changes at the population or community level (dynamics, structure)

The effects of environmental stressors start from the effects (biomarkers) to lower levels (individual, subindividual). In individuals exposed to chemical compounds (heavy metals, organic pollutants) there may be increases in biochemical biomarkers (metalotein induction, biotransformation metabolism, oxidative stress). However, when acute or chronic chemical stress exceeds compensation limits, biomarker responses are depleted and may decrease below control levels.

Ecological and ecophysiological aspects of tolerance

In a biological community exposed to toxics in a polluted environment, the most sensitive organisms are lost as a result of contaminating pressure, while the most tolerant survive. Consequently, the new community is more tolerant to the toxics responsible for the selection than another originally identical community, but has never been exposed to the toxicant.


Physiologically, the ability to tolerate increased levels of toxic substances can be expensive in terms of energy or other resources. The energy costs are due to processes that protect organisms against stressors (escape reactions, mucous barriers, protein synthesis) or contribute to eliminate the body of a stressor (metabolizing or excreting pollutants).

According to the metabolic cost hypothesis, a decrease in energy reserves (carbohydrates, lipids, proteins) is observed in different species exposed to various types of contaminants. The intensity of the impact of the stressor varies according to the species and type of stressors, due to the effect it has on different biological characteristics.

However, the adaptive benefit of tolerance has another negative counterpart to the potential cost of tolerance that leaves a system deficient to respond to additional stressors.

Referencia: Férard y Blaise (2013). Encyclopedia of Aquatic Ecotoxicology.