如果在给定的一组注册人中，有两种非常相似的物质（相同的吨位范围、相同的危害特征和相同的注册用途），其中一种入围而另一种没有入围，原因可能是什么？

如果在给定的一组注册人中，有两种非常相似的物质（相同的吨位范围、相同的危害特征和相同的注册用途），其中一种入围而另一种没有入围，原因可能是什么？

If in a given group of registrants, there are two very similar substances (same tonnage band, same hazard profile and the same registered uses) and one of them was shortlisted and the other one was not, what could be the reason for that?

ECHA 正在努力识别物质之间的关系，并构建由同一成员国同时进行评估的物质组。然而，两种相似的物质确实有可能在不同时间进行评估，例如，如果其中一种物质目前正处于监管行动中，无法进行评估，例如等待测试结果或风险管理方案分析的结论。我们的物质分组算法也可能无法识别某些结构关系，尤其是对于那些定义不明确的物质。

­ECHA is trying to identify relationships among substances and construct substance groups that are to be evaluated together and at the same time, by the same Member State. However, it is possible that two similar substances are indeed evaluated at different times, if for example for one of the substances there are ongoing regulatory actions that prevent evaluation at the moment, such as awaiting the outcome of a test or the conclusion of a risk management option analysis. It is also possible that our substance grouping algorithms failed to identify certain structural relationships, especially for substances that are not well-defined .