Two North Lanarkshire schools sharing the same site: Buchanan High School and St Ambrose High School, hit the Sunday Post and other newspapers recently over the presence of tap water stained blue. This is thought to be due to a reaction with copper pipework. Alongside this, pupils and teachers have reported multiple health concerns, ranging from headaches and nausea, to blindness and even cancer.
There is suspicion that the blue tap water and health concerns are related to the former use of the site as an industrial landfill site. Those concerned suggest that this led to high levels of copper and other environmental agents (such as arsenic, lead, and nickel) at the site.
North Lanarkshire Council and NHS Lanarkshire stated that there is no cause for worry. However, due to ongoing levels of public concern, the Scottish Government have ordered an independent review of the circumstances. This will be led by the Scottish Government Chief Planning Reporter and a specialist in public health. The review will assess the public health measures and information provided in response to the concerns. It will also examine whether risk assessment and works were carried out in accordance with appropriate regulations and following best practice to reduce risk to public health. BBC news reported that this will include testing the water and grounds for contamination.
Looking for a cause
So, how do we know if the reported health concerns are due to high levels of environmental agents linked to the site’s former use?
First, evidence is needed on the levels of environmental agents at the site of the schools to assess whether these are abnormal. Secondly, it must be shown that the environmental agents are the cause of the reported health concerns.
The Bradford Hill criteria can help to address the second point. These are a set of criteria for evaluating “causality”; whether a potential cause (in this case, environmental agents) is leading to an outcome (here, reported health concerns) or not. Evaluation involves assessing each criterion individually, then looking at the strength of evidence across all the criteria. Available evidence, as well as collection of new information, can be assessed.
Currently, the Scottish Government inquiry has not explicitly stated that they will use the Bradford Hill criteria, however, the concepts covered in the criteria will need to be addressed if the review aims to draw conclusions on whether the environmental agents are causing health concerns.
The nine Bradford Hill criteria are set out below, together with commentary on how they might apply to the current situation:
Temporality considers the timing of the cause and outcome in terms of which came first. In the case of the schools, if a child reported health concerns before starting at either of the schools, it would be difficult to see how the presence of environmental agents at the schools could be causing the health concern.
Strength of association
The more often a cause and outcome are seen together, the stronger the evidence is that one is causing the other. For example, if all the children with high levels of copper in their blood do report health concerns and all those with low levels of copper don’t, it seems more likely that the copper levels and the health concerns are linked. If, on the other hand, there is roughly the same amount of health concerns in children with high or low levels of copper, it is less likely (though not impossible) that copper is causing the problems.
If the cause is seen with the outcome across multiple locations and populations, we are more likely to believe that the two are linked. On the other hand, it might be that the relationship between the cause and outcome is more complex, so maybe there is a cause that only affects girls not boys.
Plausibility relates to how believable it is that the cause could affect the outcome. If someone told you that the more butter a town consumes, the more marriages there are, you are unlikely to think that one of these is causing the other. Assessing plausibility means looking at all available evidence and theories. If plausibility isn’t obvious, it doesn’t rule out causality. It may be that scientists have not yet identified how the cause and outcome are related.
The best way to test whether a cause impacts on an outcome is often to carry out an experiment, as is done using clinical trials for testing drugs. Experiments aim to show whether, if conditions are identical except for the cause, we get the same outcome. This tells us whether removing the cause is expected to change the outcome.
It’s not always possible to carry out experiments. In the case of the schools, it wouldn’t be ethical to keep some children and teachers in the school and move some elsewhere to see if the health of the groups differ. Experiments can be a little more creative in these situations, for example carrying out tests in laboratories that try to mimic the situation.
The idea of “coherence” is similar to plausibility; assessing whether our proposed cause and outcome fit with the knowledge we have. This requires exploring available scientific knowledge and our proposed cause and outcome to see whether these fit together. This could mean looking for studies where people were exposed to specific environmental agents and seeing whether any reported health concerns are similar to those reported at the schools.
This relates to the idea that the higher “dose” (or amount) of a cause, the bigger the effect on the outcome. There are examples where this doesn’t hold true, so it is not always necessary to prove this.
If there is a similar cause-and-outcome relationship to the one we are exploring, it is easier to believe that our cause-and-outcome are linked. In the case of the schools, if it’s possible to find examples of people living on previous landfill sites, where there has been evidence of high levels of environmental agents linked to reported health problems, it is easier to trust that the site of the schools may be important for reported health concerns. If there isn’t an obvious analogy, it may just be that no-one has noticed or examined a similar situation, so analogy may not be applicable in all situations.
Specificity is the idea that a potential cause is associated with one outcome. There is less support for this criterion, as it is now known that often one cause can impact many outcomes, and that sometimes it is a combination of causes, not one alone, that is important for a single (harmful) outcome.
The independent review will address management of the circumstances and concerns raised in relation to health of pupils and staff. This may involve use of the Bradford Hill criteria to assess whether the site of the schools has led to a high level of environmental agents, and whether this has caused health concerns.
The review aims to report before the start of the school term in August 2019.
Emma Butcher, PhD intern