Hydrogen sulfide, H2S, which is extremely toxic to humans, can be detected at a concentration of 2.00 ppb. At his level, headaches, dizziness, and nausea occur. At higher concentrations, however, the sense of smell is lost, and the lack of warning can result in coma and death can result. What is the concentration of H2S in mg/L at the detection level? The lethal dose of hydrogen sulfide by inhalation for rats is 7.13 X 10-4 g/L/ What is the lethal dose in ppm? The density of air is 1.2929 g/L.