Dose-Response Curve in Biocides
The dose-response curve relates the concentration of a biocide and its contact time to the effect achieved, for example how many microorganisms it kills.
In disinfection, the response is normally expressed as a log reduction: 1 log is equivalent to eliminating 90 % of the microorganisms, 4 log to reducing them 10,000-fold and 5 log to reducing them 100,000-fold. Below a certain concentration the effect is insufficient; from there it grows with the dose until it stops improving appreciably. Dose and time partly compensate for each other: a lower concentration may need a longer contact time for the same result, and each type of microorganism has its own curve. In toxicology, similar curves are used to describe effects on people or the environment (for example, the LD₅₀), which must not be confused with effectiveness.
The curve shifts with the conditions of use: organic matter, temperature, pH and water hardness can reduce or increase effectiveness. That is why disinfectant test standards set clean or dirty conditions, temperature and time, and the declared effectiveness only applies to the dose and time tested. Using less product than indicated leaves surviving microorganisms; using more does not always improve the result and increases cost, residues and the risk of damaging materials.
Instaquim technical data sheets show examples of how the dose or time changes depending on the effect sought:
- InstaBact® 3000: at 2 %, about 5 min for bactericidal effect and about 15 min for bactericidal and fungicidal effect; at 50 % and about 5 min for enveloped viruses.
- Bacter 100: 10 g/l (1 %) and about 5 min for bactericidal effect; 50 g/l (5 %) and about 15 min for bactericidal and virucidal effect against enveloped viruses.