Amidst an attempt to link the sudden spike in Zika virus cases in Brazil with microcephaly – a birth defect causing babies to be born with abnormally small heads with under-developed brains – a group of doctors and researchers at the University Network for Environment and Health are arguing an alternative theory.

They claim that a larvicide, pyriproxyfen that was released into the drinking water supply in 2014 in Brazilian towns to control the growing mosquito population is the cause for the birth defect.

While the jury is still out on what’s really causing the surge in microcephaly cases, the Brazilian Health Officials say that there is no scientific basis to prove the pesticide theory.

Still, this is not the first time that chemical water contaminants have been accused of causing birth deformities.

In 2013, the U.S. Center for Disease Control and Prevention confirmed a long-suspected link between water pollution and birth defects and childhood cancers in Camp Lejeune military base in North Carolina. Industrial spills, leaking underground storage tanks and an off-base dry cleaning center were among the sources responsible for the contamination according to the CDC.

In California’s San Joaquin Valley, high levels of nitrate contaminants that leached into the groundwater from a large toxic-waste dump site outside the city was also suspected to be linked with cleft-palates, spina bifida and other birth defects recorded in the area in 2010.

Sure, there isn’t a lot of clear evidence stacked against man-made chemicals in the water and its probable direct link to birth defects and other health issues, but it seems only logical to proactively investigate what’s really in the water and it’s implications on human health.