Across 10 cohorts and 29 lifestyle and environmental signatures, comparing tumor DNA methylation in early-onset (<50) vs late-onset (≥70) colorectal cancer, one signal stood out: the herbicide picloram. Early onset tumors showed ~3 fold higher odds of carrying the picloram methylation signature in the discovery cohort, and 1.77-fold across all 10 pooled cohorts (114 early onset vs 372 late onset).