Whether a chemical is safe is typically determined by a chemical risk assessment. Conventional chemical risk assessments consider effects on human health and effects on the environment separately. The results from animal (in vivo) studies are, often roughly, extrapolated to estimate a concentration which should be low enough to be protective. Increasingly, the results of non-animal (in vitro) studies are used to complement or replace animal studies.
A complete transition to only using the findings of non-animal studies has been a goal in chemical risk assessment for decades. Consumer calls for improved animal welfare is a significant driver for this, but there are many others:
- Non-animal tests are significantly cheaper than animal tests, because they are quicker to run and the costs in keeping animals are avoided
- Because non-animal tests are quicker to run, the findings are available sooner – and regulatory approvals can be obtained faster, where they needed, and
- Sophisticated non-animals studies may allow more accurate risk assessments and better justification for any restrictions on use.
The potential for improved accuracy in risk assessment is due to non-animal studies detecting molecular levels changes, while animal studies allow us to see changes at the organism level only. For example, a non-animal study may detect the gene mutation that leads to cancer, but in an animal study we would only see the resulting tumour. The cause of the tumour would be unknown, so we would not be sure how relevant the finding is more broadly. But if we know what the original mutation is, we could say that all species which have that gene are at risk – at least in theory.
It is the idea that non-animal studies could provide insights that have relevance across all species that has led to a bigger goal of integrating the human health and environment aspects of chemical risk assessment. However, a lot of work is required for this to become a reality. If we don’t know which species carry the gene identified in the above example, the findings become much less useful. There are many significant data gaps that would need to be filled before this could become a reality.
A recent paper from 28 scientists summarises the outcomes of a workshop held to discuss these issues. They agreed that while progress has been made, there are still a number of barriers. A key barrier is that many non-animal tests are not currently acceptable for regulatory approvals. They acknowledge that this is a ‘chicken and egg’ issue. Further investment is difficult to justify when regulators are not accepting these tests, but regulators are unlikely to change their stance until there is more certainty.
The title of the paper suggests that integrated chemical effects assessments fully based on the findings of non-animals studies are a possibility in the near future. I hope so, but am yet to be convinced – especially on the environmental side of things. A huge amount of work is needed before non-animals studies will be able to provide a level of assurance that is equivalent to the data currently required by chemical regulators.