In this paper we establish a baseline to use Stentor coeruleus, a freshwater single cell ciliate, as a chemical biosensor. We expose Stentor to an array of chemical species and concentration and monitored morphological and dynamic responses. We developed a computer vision pipeline to predict chemical exposure at sub-lethal doses. We present analysis for butylparaben, a common antimicrobial preservative used in cosmetics and food flavoring. Our preliminary results show high sensitivity of Stentor to sublethal chemical concentrations, amenable for use as an environmental biosensor when combined with the computer vision pipeline.