Exposure to titanium and nickel as the novel risk factors for PCOS: Evidence from a case control study in Xiamen, China - Zhineng Fu; Lanlan Liu; Jingyi Wang; Fengkai Ruan; Yurong Chen; Liying Zhou; Chunyan Yang; Jiali Cai; Runzeng Liu; Chengyong He; Xiaoming Jiang; Zhenghong Zuo (Journal of Environmental Sciences, 2026)