Comments on "arsenic release provided by MTA and Portland cement" by Duarte MA, et al.

The authors presented their data from atomic absorption tests, stating that the cements released less than 0.0007 ppm of arsenic after a week of soaking in weakly acidic solution. That is, the cements released 0.7 ppb from their worst sample. My first comment is on the atomic absorption technique for arsenic. According to the EPA method 7062 for detection of arsenic by atomic absorption using sodium borohydride reduction, the typical detection limit is 1 ␮g/L, which is equal to 1 ppb. These authors are reporting amounts below the normal detection limit for the same method used by the EPA. How did they achieve such results? Second, on page 649, the LD 50 is listed two times for sodium arsenate as 600 mg/kg and also as 10-50 mg/kg. Which is correct? Should one of these have been sodium arsenite? Also, the authors state that they quantified trivalent arsenic, but was any pentavalent arsenic (arsenate) neglected in their analysis? Or did their analysis technique convert all pentavalent to trivalent arsenic? This should have been clarified for the reader. Third, the authors did not report the total arsenic content of the cement they tested. In a report from the Forschungszentrum Karlsruhe GmbH, the average arsenic content of 417 Portland cements was 6.8 ppm. Another study cited in this report found an average of 33 ppm of arsenic. Fourth, the authors did not validate their choice of a solution with a pH equal to 5, nor did they mention any of the dental standards that have solubility requirements to measure As. For instance, ISO 9917, entitled Dental Water-based Cements, has a requirement for lead and arsenic that is appropriate for the Portland cement and ProRoot MTA materials. In ISO 9917, the leachable lead and arsenic must be less than 100 ppm and 2 ppm, respectively. The leaching method is to use hardened, but crushed, cement in a 20% HCl solution for 16 hours. Such a solution has a pH less than 1, considerably more acidic than the authors used. Thirty-six mole percent hydrochloric acid is specified for solubility testing for arsenic in ADA 30 for zinc oxide-eugenol cement. The weakly acidic solution used by the authors did not equal the acidity of vinegar (pH of about 3). Four percent acetic acid, similar to vinegar, is the standard used in testing the solubility of dental porcelain (ISO 9693), not cements. Fifth, Portland cement for construction …