Amalgam Risk Assessment pt2 Excessive Concurrent Exposure to Pb, MeHg and Hg0 in US population.


Mark Richardson P.h.D. explains part 2 of the amalgam risk assessment he presented to the FDA

Mark Richardson, PhD, of SNC Lavallin, Ottawa, Canada, formerly of Health Canada, provided the scientific panel and FDA regulators with a formal risk assessment using the latest information from the scientific literature. Part 2 is titled CUMULATIVE RISK ASSESSMENT AND JOINT TOXICITY: MERCURY VAPOR, METHYL MERCURY AND LEAD

Regulatory guidance for evaluating potential cumulative risks from concomitant exposure to chemical mixtures was reviewed. Following this guidance, the toxicological and related data were evaluated for mercury vapour (Hg0), methyl Hg and lead (Pb). That evaluation focused onreported similarities in individual and combined target organ, mechanism of action,toxicokinetics and toxicodynamics for these substances. This information and the potential for combined exposures to these substances were considered in order to determine if risks associated with the concurrent exposures to these metals should be evaluated jointly, rather than independently as is currently practiced.

Concurrent exposure to Pb, MeHg and Hg0 does occur in the US population. A large proportion- 1/3rd – of the US population is concurrently exposed to Hg0, methyl Hg and Pb on a daily basis.All of these substances share the following characteristics:

  • All are absorbed in large proportion into systemic circulation;
  • All cross the blood-brain and placental barriers;
  • All cause neurological toxicity;
  • Exposure to all of these substances currently exceed individual reference exposurelevels for many in the US population.

The weight of available evidence suggests that risks posed by concurrent exposure tocombinations of these 3 substances should be assessed as additive.

UPDATE 2/14/2011 From Mark Richardson:

mark-richardson-01I indicated during our interview that ATSDR considers amalgam to be ‘safe’. This is based on my overall interpretation of ATSDR’s failure to update their toxicological profile since 1999, and their failure to consider mercury vapour in any of their Interaction (mixtures) profiles. Here is what the ATSDR Interaction Profile for Chlorpyrofos, Lead, Mercury and Methylmercury states:

Some absorption of metallic mercury occurs from dental amalgam fillings, probably following volatilization from the fillings. Clear evidence of adverse effects from this pathway of exposure is lacking, as are joint action studies with the other components of this mixture, so this form of mercury is not considered further in the interaction profile. The critical effect of inorganic mercury is on the kidney, which is not a sensitive target organ for the other components of the mixture.

It is apparent that ATSDR does not recognize any potential for adverse effects from exposure to Hg0, whether from amalgam or any other source. Further, ATSDR appears to suggest that the main target organ is the kidney rather than the central nervous system (CNS), which is incorrect. The NHANES data provide direct and unambiguous (clear) evidence of simultaneous exposure to Hg0 and Pb and MethylHg in 122 million Americans. Therefore, it is evident to me that the omission of Hg0 from the ATSDR’s Interaction Profile for Chlorpyrofos, Lead, Mercury and Methylmercury was based on factors other than data and evidence.
Mark Richardson

{slide=How the USA amalgam risk assessment came about}

mark-richardson-01Late 2009, while Mark Richardson was still at Health Canada he was contacted by Michael Adjodha of the Food and Drug Administration (FDA) who was seeking some clarifications about his 1995 Risk Assessment for Health Canada and about his recently (at that time) published article on mercury vapour and setting the reference exposure levels (REL) for mercury. During those phone conversations with Adjodha, Mark answered various questions about his research and publications; the details of which he admits are vague at this point.

In April 2010 Mark Richardson had moved on from Health Canada to SNC-Lavalin. Not long after the move Adjodha contacted Mark again, following up with him about the same issues. Adjodha then pitched the idea of Mark becoming a ‘special employee’ (basically a temporary fulltime staffer) with FDA to assist them with preparations for the planned expert panel and perhaps some follow up. While Mark was interested, it turned out that it would require a green card to work for the US government; a green card Mark did not have, so the idea was eventually abandoned.

Mark decided to put together an unsolicited proposal to complete an up-to-date risk assessment of mercury exposure from dental amalgam for the US population, as it was apparent that this would be relevant and useful (perhaps critical) to an effective evaluation by the Expert Panel. Mark ultimately sent two proposals to Adjodha via email, dated June 29, 2010.

  • Proposal 1 was for part 1 of the report (Hg exposure in US population);
  • Proposal 2 was for the review of concomitant exposure to Hg0, MeHg and Pb (part 2 of the report).

While Adjodha responded favorably to the idea and the need for this work, there were high costs involved ($116K in total), and the fact that Mark was Canadian and not a US citizen. Additionally, Adjodha could not have FDA fund the risk assessment via sole source (no competition). If FDA were to try and fund the risk assessment, Adjodha (FDA) would have to post an open request for proposals and could award it to Mark only if he were the lowest bidder. Since, this RFP process would take months it would miss the deadline for submission to and consideration by the expert panel. Adjohda indicated that if Mark could find an alternate funding agency or organization, and could get the reports to him no later than November 14, 2010, Adjohda would submit them as part of the information package for consideration by the expert panel.

Mark then sent the proposals to the International Academy of Oral Medicine and Toxicology* (IAOMT) who opted to fund them (this is now late August). As a result, Mark and his team got started in early September and got the work done and delivered to the FDA by the November 14th deadline. True to his word, Adjodha included the reports in the package of studies and information to be considered by the expert panel. As part of the contract with IAOMT, Mark flew to Washington DC, in Dec 2010 to briefly present the results to the FDA dental products panel.

* IAOMT was actually the contract manager; funding came from two charitable / not-for-profit foundations. IAOMT merely managed the disbursement of funds once the work was completed.{/slide}

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