From the US Environmental Protection Agency:
EPA identified these chemicals at this time for a variety of reasons, similar to those it used to identify the seven Work Plan chemicals to assess in 2012. The 18 chemicals span the range of the Work Plan screening criteria, including some chemicals associated with specific hazards such as potential carcinogenicity or reproductive or developmental toxicity; chemicals presenting persistent, bioaccumulative, and toxic potential; and chemicals found in biomonitoring or reported in consumer products. Some of these chemicals, such as the five chlorinated hydrocarbons, the three flame retardants, and the four fragrance chemicals, may present an effective opportunity to assess groups of related chemicals together.
The list of chemicals up for assessment can be found at the above link.