Herein we describe a miniaturised chemical toxicity analyser with capacity to assess water quality without intervention of laboratory equipment. The device, as presented, integrates living cells and electrode-based sensors to monitor cell viability upon exposure to toxic chemicals. The methodology involved cultured fish cells Poeciliopsis lucidia hepatocellular carcinoma (PLHC-1) and Oncorhynchus mykiss rainbow trout gonad (RTG-2) cells, exposed to toxic chemicals (CdCl2 and pentachlorophenol (PCP)) after which the activity of a cellular enzyme, acid phosphatase (AP) was measured. Reduced AP activity was quantified electrochemically, allowing IC50 values (50% reduction in AP activity) to be determined. Fish cells are a relevant model of the toxicity risks posed by contaminated water to aquatic health. Such cells are relatively slow growing and do not require a source of CO2 for incubation, thus ensuring portability for single-use point of site applications. The 24 hour IC50 values determined for CdCl2 in the fish cell lines (16.2 ± 0.7 and 91 ± 11 μM for PLHC and RTG-2, respectively) were in agreement with those found using the MTT assay (16.3 ± 1.6 and 164 ± 96 μM). In the case of PCP, the IC50 value in PHLC cells (127 ± 22 μM) suggested enhanced sensitivity towards PCP compared with the MTT assay (IC50 > 160 μM). The optimised electronic assay was transferred to a prototype integrated assay cartridge with associated fluidic and transducer elements. This device (TOXOR) monitored changes in the metabolic state of fish cells, realising high-value toxicity information as a potential early warning on-site screening system.