The province has launched a new investigation into the hundreds of cases, saying the symptoms have sparked fear among many New Brunswickers that needs to be addressed.
Moncton neurologist Dr. Alier Marrero has suggested that glyphosate has contributed to blue-green algae blooms that can emit toxins that affect the brain.
"New Brunswickers are afraid about what glyphosate might do, and the mysterious neurological illness has given them reason to be more afraid," Holt said in a year-end interview with CBC News.
"So we have to make sure that we know exactly what that chemical is doing, and where and when."
If a link is found, "then we need to eliminate that exposure for New Brunswickers."
But Holt emphasized "we don't have good science to tell us that that is what's making New Brunswickers sick."
Chris Edge, the lead researcher on a 2023 study, said glyphosate is present in the environment but at low levels.
Edge said algae can feed on phosphate molecules in glyphosate, "but for that to work, glyphosate would have to be present in the rivers," and his study found it in only one sample.
"So [it's] theoretically plausible, but in reality we're not detecting glyphosate, so it's unlikely to be leading … to cyanobacteria blooms,” he said.
Sarah Nesbitt, one of Marrero's patients whose urine samples showed levels of glyphosate, said she believes the herbicide and a mix of other environmental factors contributed to her illness.
