Dispelling urban myths about default uncertainty factors in chemical risk assessment - Sufficient protection against mixture effects?

© 2013 Martin et al.; licensee BioMed Central LtdThis article has been made available through the Brunel Open Access Publishing Fund.Assessing the detrimental health effects of chemicals requires the extrapolation of experimental data in animals to human populations. This is achieved by applying a default uncertainty factor of 100 to doses not found to be associated with observable effects in laboratory animals. It is commonly assumed that the toxicokinetic and toxicodynamic sub-components of this default uncertainty factor represent worst-case scenarios and that the multiplication of those components yields conservative estimates of safe levels for humans. It is sometimes claimed that this conservatism also offers adequate protection from mixture effects. By analysing the evolution of uncertainty factors from a historical perspective, we expose that the default factor and its sub-components are intended to represent adequate rather than worst-case scenarios. The intention of using assessment factors for mixture effects was abandoned thirty years ago. It is also often ignored that the conservatism (or otherwise) of uncertainty factors can only be considered in relation to a defined level of protection. A protection equivalent to an effect magnitude of 0.001-0.0001% over background incidence is generally considered acceptable. However, it is impossible to say whether this level of protection is in fact realised with the tolerable doses that are derived by employing uncertainty factors. Accordingly, it is difficult to assess whether uncertainty factors overestimate or underestimate the sensitivity differences in human populations. It is also often not appreciated that the outcome of probabilistic approaches to the multiplication of sub-factors is dependent on the choice of probability distributions. Therefore, the idea that default uncertainty factors are overly conservative worst-case scenarios which can account both for the lack of statistical power in animal experiments and protect against potential mixture effects is ill-founded. We contend that precautionary regulation should provide an incentive to generate better data and recommend adopting a pragmatic, but scientifically better founded approach to mixture risk assessment. © 2013 Martin et al.; licensee BioMed Central Ltd.Oak Foundatio

Condrossarcoma laríngeo: relato de caso e revisão de literatura Laryngeal chondrosarcoma: a case report and review of literature

Os tumores cartilaginosos da laringe são extremamente raros e correspondem a aproximadamente 1% dos tumores que acometem este órgão. Menos que 0,1% destes tumores correspondem aos condrossarcomas. Os condromas e os condrossarcomas de baixo grau são os mais freqüentemente encontrados e 70-75% destes tumores localizam-se na face laríngea da lâmina posterior da cartilagem cricóidea. O diagnóstico do condrossarcoma da laringe pode ser esquecido devido a sua baixa ocorrência e sua forma indolente de crescimento. A apresentação clínica é variada e diretamente dependente do tamanho e localização do tumor: estridor, cornagem, dispnéia, disfagia ou massa cervical são os sinais mais freqüentes. O objetivo deste estudo é apresentar um caso incomum de condrossarcoma laríngeo de origem na cartilagem tireóidea, discutindo o quadro clínico, o diagnóstico, tratamento e os fatores prognósticos.<br>Cartilaginous tumors of the larynx are extremely rare neoplasms that account for approximately one per cent of all tumors of this organ. Less than 0.1% correspond to chondrosarcomas. Chondroma and low-grade chondrosarcoma are the most common, 70-75% of these tumors arise on the endolaryngeal surface of the posterior lamina of the cricoid cartilage. The diagnosis of laryngeal chondrosarcoma is likely to be missed because of its infrequent occurrence and its indolent pattern of growth. The clinical presentation is varied and directly dependent on size and location of tumor: stridor, hoarseness, dyspnea or neck mass are commonly presented signs. The objective of this study was to show an unusual case of laryngeal chondrosarcoma originating from thyroid cartilage, discussing its clinical presentation, diagnosis, treatment and prognosis