What is one of the main challenges with detecting sub-lethal impacts of oil exposure?

One of the main challenges with detecting sub-lethal impacts of oil exposure is that animals may visually appear to be normal. This means that even though an organism is exposed to oil, it might not exhibit obvious signs of distress or impairment, making it difficult for researchers to identify the effects on their health. Sub-lethal impacts can manifest as changes in behavior, reproductive success, or overall fitness, which may not be apparent without more in-depth physiological or ecological study. Therefore, since the external appearance of the animal does not change, it poses significant challenges in assessing the true extent of the damage caused by oil exposure.