Hello,
I thought that Threshold limit values (TLVs) or Permissible exposure values (PELs) are key parameters to monitor which substance i.e, pigment is more toxic. Pigments/metals with lower TLVs are more toxic. Am I right? Therefore lower TLVs call for stricter/lower mass to space (mg/m3) contamination. Time weighted average (TWA) defining time interval in which this TLV or PEL is averaged.
Lately, I started considering to use PW1 (lead carbonate) and find out that I cannot buy and use it for producing easel paintings. I live in EU. But cobalt and cadmium can easily be bought in the same market space.
Let us consider PELs for these three meatls, the NIOSH CDC pocket guide to chemical hazards lists:
Cobalt metal dust, Cobalt metal fume-OSHA PEL TWA 0.1mg/m3,
Lead metal, Plumbum-OSHA PEL TWA 0.050 mg/m3,
Cadmium metal-OSHA PEL TWA 0.005 mg/m3.
From this data it looks like cadmium is more dangerous than other two. I know that there can be difference in PELs regarding size of particulates (inhalable, repirable), but this is all I found. Why is then lead so dangerous that it needs special regulations?
Please can anyone clarify this very important topic?
Damir P.
Thank you very much.
I will let others comment on the nomenclature, but I want to first state that it is more complicated that that. Toxicity of cadmium metal is a separate issue than the toxicity of a cadmium pigment. It would depend on how much free cadmium is in the pigment. Most high quality cadmium pigment has little or no free cadmium.
Brian is correct; this is more complicated than can be addressed simply here. The first item to consider is that cadmium metal has different toxicity than cadmium sulfide which is the chemical compound of the pigment. This is also true for lead and cobalt—the metals are different from the pigments. Second, the route of exposure must also be considered. Titanium dioxide is considered to be a carcinogen (at least by the state of California), but only through inhalation. It can be applied to skin and even consumed. Third, the purity of the substance is another factor to consider. Most cadmium pigments today are very pure substances and hence are essentially insoluble, so they present less danger in their intended applications. Lead white, which is basic lead carbonate, is also insoluble, but in the presence of acid, it can form different compounds such as lead acetate which is soluble in water and hence is very toxic if ingested.
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