Aschengrau Weinberg Janulewicz 2012

The risk ratio (RR) was used to estimate the strength of the association between PCE exposure and the occurrence of each illness. Ninety-five percent confidence intervals were used to assess the precision of the risk ratios.

The risk ratio (or relative risk) is a statistical method used to show the ratio of probability of an outcome in a group exposed to a specific treatment or risk factor relative to an unexposed group. In mathematical terms this is the incidence rate (of the outcome) of the exposed group divided by the incidence rate of the unexposed group. In this case the exposed group are individuals exposed to PCE (tetrachloroethylene) in their drinking water prenatally and/or during early childhood and the unexposed group is individuals of a similar demographic composition who were not exposed to PCE. The ninety-five percent confidence intervals refer to the confidence level that a range of values likely to contain the true values (95% is usually used to eliminate significant statistical outliers). For example “RR 2.7, 95% CI: 1.3-5.6” indicates a mean risk ratio of 2.7 with 95% of the observed population falling into the confidence interval of 1.3-5.6. Therefore in 95% of the observed population exposed individuals have a 1.3-5.6x incidence of developing the outcome compared to unexposed individuals with an average of 2.7x.

We undertook a population-based retrospective cohort study to examine the long-term neurotoxic effects of prenatal and early childhood exposure to PCE contaminated drinking water.

Here “population-based” refers to a specific group of people, and “retrospective cohort” refers to following similar groups of people who have a common exposure factor and observing changes over time in comparison to non-exposed individuals. Putting this all together this means observing the long-term damage to the brain in people who have or have not been exposed to PCE contaminated drinking water before birth or during early childhood within a specific population

When exposure levels were examined, subjects in the highest exposure tertile had further increases in the risk ratios for bipolar disorder (RR 2.7, 95% CI: 1.3-5.6) and post-traumatic stress disorder (RR: 1.7, 95% CI: 0.9-3.2).

“Tertile” here refers to one of three groups that the subjects were split into based on amount of PCE exposure (high, medium, or low levels). This means that the more PCE exposure they had early in life, the more likely they were to develop bipolar disorder and/or PTSD as an adult (roughly 1.5-fold and 1.13-fold increase respectively based on data presented earlier in the results section).

While the mechanism by which PCE might cause neurotoxic effects is currently unknown [3], there is evidence to support mechanisms involving the peroxidation of cell membrane lipids [29], alterations in the fatty acid profile of the brain [30], and loss of myelin [31], and interactions with neuronal receptors [32].

This is discussing how the neurotoxic effects of PCE damage the central nervous system indicating oxidative degradation of the phospholipid bilayer in the cell membrane, change to brain lipid structures, loss of myelin (neuronal axon sheathing for protection and added efficiency), and changes in the way neurons interact with other cells.

A direction of future research that I would think would be illuminating is the addition of another follow up study with the same population of individuals when they are older or even geriatric. It is often not until later in life that development of central nervous system conditions like Parkinsons and Alzheimer’s disease occur. Given the known neurotoxicity of PCE and the areas it damages I would anticipate that conditions such as these would be more prevalent or have an onset earlier in life for exposed individuals.

The parts of this paper that I struggled the most with regarded the geocoding and exposure distributions of PCE in drinking water supplies. While I have experience with medical data and statistical models, I have no knowledge of how chemical leaching rates are determined and mapped.