An innovative and timely topic will be to study the impact of the antibiotics in the underground drinking water on increased resistance to antibiotics. This subject may seem unfeasible but with proper location of a natural experiment, it is possible. I will be happy to elaborate if needed.
The geographic distribution of some diseases and relating that to soil/mobile sand/ dust/ aerosols properties should be tackled in a wider scale (regional or global) studies. As we found some such as:
Pollen associated with dust in relation to number of allergy patients (Article Pollen in aeolian dust with relation to allergy and asthma in Kuwait) (https://link.springer.com/article/10.1007%2Fs12517-015-2182-z
(PDF) Pollen in aeolian dust with relation to allergy and asthma in Kuwait (researchgate.net)
Also high cancer within some plutonic/igneous/metamorphic rocks regions compared to sand dunes regions.
Many geographical regions have presence of trace and heavy metals in geological rock formations and may get into medium creating potential health risk. Like As,F, chromium,cd etc may result in health risk to community and need to be thoroughly investigated.