Traces of pesticides that act as nerve agents on bees have been found in 75 percent of honey worldwide, raising concern about the survival of these crucial crop pollinators, researchers said Thursday.

Human health is not likely at risk from the concentrations detected in a global sampling of 198 types of honey, which were below what the European Union authorizes for human consumption, said the report in the journal Science.

However, the study found that 34 percent of honey samples were contaminated with “concentrations of neonicotinoids that are known to be detrimental” to bees, and warned that chronic exposure is a threat to bee survival.