Discuss the difference between nonthreshold chemicals and th

Discuss the difference between non-threshold chemicals and threshold chemicals and their comparative dose-response curves.

Solution

                              1)   Threshold and Non threshold chemicals

Genotoxic-Which causes induction of mutations in the genetic material (DNA). These genotoxic does not have a threshold.

Here is a probability of harm at any level.

mathematical low-dose risk extrapolation is applied.

Non genotoxic- some carcinogens acting through an indirect mechanism are capable of producing tumors in animals or humans without exerting genotoxic activity.

These non genotoxic have a threshold.

IARC assigns chemical substances with respect to their potential carcinogenicity into the following categories:

Group 1: The agent is carcinogenic to humans.
Group 2A: The agent is probably carcinogenic to humans.
Group 2B: The agent is possibly carcinogenic to humans.
Group 3: The agent is not classifiable as to its carcinogenicity to humans.
Group 4: The agent is probably not carcinogenic to humans.

EXAMPLES

Non-threshold genotoxic carcinogens- Some PLATINUM SALTS, VINYL CHLORIDE, 1,3-BUTADIENE, METHYLENE DIANILINE, DIMETHYL SULPHATE

Genotoxic carcinogens for which a threshold cannot be sufficiently supported at present- HEXAVALENT CHROMIUM COMPOUNDS, BENZENE, WOOD DUST, BERYLLIUM

Genotoxic carcinogens with a practical threshold- NICKEL, CADMIUM, VINYL ACETATE, FORMALDEHYDE, NITROBENZENE, PYRIDINE, SILICA, NAPHTALENE

Non-genotoxic carcinogens- CHLOROPHORM, PHENOL, CARBON TETRACHLORIDE

                                                        2) Dose response curve