Water quality dictates arsenic migration from raw paddy to cooked rice through the traditional parboiling and cooking process: a complete intrachain assessment in the Bengal Delta.

Arsenic (As) contamination in rice is a major dietary exposure risk in South and Southeast Asia, yet As migration during traditional rice processing remains poorly resolved. This study presents the first continuous, integrated assessment of As migration from raw paddy (RP) to cooked rice through parboiling (steaming, soaking, and boiling) and cooking. Ten independently collected raw paddy (RP) samples representing eight rice cultivars (range: from 144 to 387 µg/kg As) and seven groundwater sources spanning safe to extreme contamination (range: < 3-450 µg/L As) were examined. Total As concentrations were quantified in intermediate paddy fractions including steamed paddy (STP), soaked paddy (SOP), and boiled paddy (BP); final edible fractions including parboiled rice grain (PRG) and cooked rice grain (CRG); and discarded processing waters including steamed water (STW), soaking water (SOW), boiling water (BW), and total discarded water (TDW). Parboiling substantially amplified As retention, with boiling identified as the dominant accumulation stage, increasing BP As from 193 to 759 µg/kg across the water contamination gradient. Although discarded waters removed considerable As (STW 20-315 µg/L, SOW 16-341 µg/L, and BW 28-345 µg/L), removal efficiency declined sharply with increasing water As. Cooked rice grain exhibited a very strong positive linear relationship with raw water As (Pearson's r = 0.9722, p = 0.0002 increasing from 152 µg/kg under As-safe water (< 3 µg/L) to 813 µg/kg at 450 µg/L. Strong predictive relationships were observed for PRG (R2 = 0.9730), CRG (R2 = 0.9452), and TDW (R2 = 0.9327). Integrated intrachain analysis revealed that when contaminated groundwater was used throughout the traditional processing sequence, the overall processing sequence was associated with higher grain As concentrations despite the concurrent removal of As in discarded processing waters. In contrast, consistent use of groundwater containing < 3 µg/L As (referred to as As-safe water in this study) achieved up to a 46% reduction in total arsenic from RP to CRG, highlighting the importance of using low-arsenic water throughout traditional parboiling and cooking.