tailieunhanh - Toxicological Risk Assessment of Chemicals: A Practical Guide - Chapter 5

Ảnh hưởng sức khỏe bất lợi có thể được coi là để trở về hai loại (xem Phần ): Những người coi để có một ngưỡng, hiệu ứng As''threshold Được biết đến''(như vậy ảnh hưởng như, ví dụ như, cơ quan cụ thể, thần kinh, miễn dịch, không genotoxic gây ung thư, sinh sản, phát triển), và Những người nào có cho Được coi là để trở Một số rủi ro ở cấp nào, biết as''non-ngưỡng hiệu ứng''(như vậy ảnh hưởng như, ví dụ như đột biến, genotoxicity, genotoxic gây ung thư) | 5 Standard Setting Threshold Effects Adverse health effects can be considered to be of two types see Section those considered to have a threshold known as threshold effects effects such as . organ-specific neurological immunological non-genotoxic carcinogenicity reproductive developmental and those for which there is considered to be some risk at any exposure level known as non-threshold effects effects such as . mutagenicity genotoxicity genotoxic carcinogenicity . Though it is not possible to demonstrate experimentally the presence or absence of a threshold differences in the approach to the hazard assessment of threshold versus non-threshold effects have been adopted widely. The distinction in approaches is based primarily on the premise that simple events such as in vitro activation and covalent binding may be linear over many orders of magnitude . that these events occur even at very low exposure levels. However a simple pragmatic distinction on this basis is increasingly problematic as it is likely that there is a threshold for a number of genotoxic effects this is addressed in detail in Chapter 6. In the hazard assessment process described in detail in Chapter 4 all effects observed are evaluated in terms of the type and severity adverse or non-adverse their dose-response relationship and the relevance for humans of the effects observed in experimental animals. For threshold effects a No- or a Lowest-Observed-Adverse-Effect Level N LOAEL or alternatively a Benchmark Dose BMD is derived for every single effect in all the available studies provided that data are sufficient for such an evaluation. In the last step of the hazard assessment for threshold effects all this information is assessed in total in order to identify the critical effect s and to derive a NOAEL or LOAEL for the critical effect s . The approach of deriving a tolerable intake by dividing the N LOAEL or alternatively a BMD for the critical effect s by an assessment factor has been