Your fallacy is: Relative Privation. It's not BLM's responsibility to "acknowledge" your point, and it's not even their responsibility to prioritize this specific issue in a way that you prefer. BLM's priorities also don't prevent anybody, such as yourself, from getting involved in environmental justice groups that are active in pursuing the lead-crime connection.

While lead may be implicated in the situation(s) that caused BLM to arise, it's not anything anybody can do anything about more than activism in terms of Flint, et al. That said, do you know who Nayyirah Shariff is?

Out of curiosity, what exactly is your goal in pursuing your line of logic, of needing "BLM" to "acknowledge" lead's role? What outcome would you like to see?