The mercury in the fish

When a family asks whether the fish on their dinner plate might be harming their child, they are asking a deceptively simple epidemiologic question. They are really asking: is the exposure real? Is the outcome real? And does the exposure actually shape the outcome?

Every one of those three questions is harder than it looks. Our team at UTHealth Houston has spent the last fifteen years working with Jamaican colleagues on the Epidemiological Research on Autism in Jamaica (ERAJ) program, trying to answer them with the kind of care that holds up to replication.

What ERAJ actually studies

ERAJ recruits young children in Jamaica with autism spectrum disorder and matches each case with a typically developing child of the same age and sex. We measure things like blood concentrations of mercury, arsenic, lead, cadmium, manganese, and aluminum. We also catalog what the children eat, where their families get their drinking water, and which genetic variants they carry in the glutathione-S-transferase family, genes that help the body clear exactly these kinds of toxicants.

The central question is not "does mercury cause autism?" That framing skips several steps. The question we can actually answer is narrower: among children with and without ASD in this specific population, does blood mercury differ in a way we can link to dietary seafood, after accounting for everything else?

Three habits that changed our answers

Three patterns recur across our papers.

Diet dominates. Children whose families ate seafood more frequently had meaningfully higher blood mercury concentrations, and the dose-response pattern was consistent across our 2013 seafood paper and its follow-ups. The effect was not subtle. This is true of arsenic and cadmium as well, where drinking-water source and consumption of fruits, grains, and vegetables all shape blood levels.

Genes modify what exposure does. Our work on GSTT1 and GSTM1 genotypes shows that the same blood manganese concentration associates with ASD differently depending on which polymorphisms a child carries. Environmental epidemiology without genotyping misses this entirely. A child with one genotype looks "exposed but fine" while a child with another looks "exposed and affected," and the average across both can come out null.

Comorbidities co-travel. Eczema, food allergies, and GI symptoms all show up more often in ASD, and they interact with the same GST polymorphisms that modify heavy-metal effects. We published this as a series of papers between 2022 and 2024. The point is not that eczema causes autism. It is that immune dysregulation and metal detoxification capacity share biological machinery, and pretending those machines run in separate rooms is how we end up with contradictory papers.

What "rigor" actually means in a field like this

Rigor in this kind of research is boring. It looks like:

1. Case-control matching that is actually matched. Matching by age and sex is not enough if the ASD and control children come from different neighborhoods with different water, different food access, and different exposure sources. Our matching protocol is deliberately expensive.
2. Sensitivity analysis that could embarrass you. If your effect vanishes when you restrict to children with complete dietary data, the paper needs to say so.
3. Replication across populations. We have extended the ERAJ framework to a Pakistani cohort and compared findings. Effects that replicate are the ones that matter.
4. Authorship norms that reward the people doing the data work. Every paper in ERAJ is a team paper. The data manager who noticed that three reported dietary values were physically impossible deserves the same consideration as the PI who framed the question.

Why this matters outside our niche

The methodological lessons from ERAJ carry outside autism research. They apply to any question where an environmental exposure shapes a developmental outcome in children, and where the exposure, the outcome, and the biology connecting them are all partially observed. That covers air pollution and asthma, pesticide exposure and neurodevelopment, microbiome disruption and GI disease.

In every case, the answer to "does X cause Y in kids?" is almost always: "under these conditions, in this population, with these genotypes, when we account for these pathways, here is what the data can say, and here is what it cannot."

That framing is less satisfying than a headline. But it is what the data can actually support. And over time, paper by paper, it is what has shifted how we interpret environmental-exposure research in child development.

Rahbar MH, Samms-Vaughan M, Loveland KA, Ardjomand-Hessabi M, et al. (2013). Seafood consumption and blood mercury concentrations in Jamaican children with and without autism spectrum disorders. Neurotoxicity Research.DOI: 10.1007/s12640-012-9370-3

Rahbar MH, Samms-Vaughan M, Ardjomand-Hessabi M, et al. (2012). The role of drinking water sources, consumption of vegetables and seafood in relation to blood arsenic concentrations of Jamaican children with and without autism spectrum disorders. Science of The Total Environment.DOI: 10.1016/j.scitotenv.2012.07.059