For decades, families across a swath of southeast Los Angeles County have lived in an environmental disaster zone, their kids playing in yards polluted with brain-damaging lead while they wait on a state agency to remove contaminated soil from thousands of homes. Now, the cleanup faces even greater uncertainty. A bankruptcy plan by Exide Technologies, which operated the now-closed lead-acid battery smelter in Vernon that is blamed for the pollution, would allow the site to be abandoned with the remediation unfinished.