Drcii

The sediment samples for trace metals analysis were freeze-dried under −80°C for 36 hours and then ground to powder using an agate mortar and pestle and passed through a 180-mesh nylon sieve to remove large particles. The screened sample was collected in acid-rinsed glass vials and stored in desiccators. 0.1000 ± 0.005 g of sediment sample (dry weight) was put into acid-washed PTFE vessel and digested with the method of HNO₃ + HClO₄. Sample was diluted to 50 mL with Milli-Q water (National Standard of China, GB 17378.5-1998). Sample solutions were analyzed for Zn using flame atomic absorption spectrometry (FAAS, SOLAAR M6, Thermo Electron) and for Cr, Pb, Cu, and Cd using Graphite Furnace Atomic Absorption Spectrometer (GF-AAS, SOLLAAR M6, Thermo Electron) and for Hg and As using inductively coupled plasma mass spectrometry (ICP-MS) (DRC-II, Perkin Elmer, USA). 0.200 ± 0.005 g of freeze-drying of benthic animals sample was put into acid-washed PTFE vessel and digested with the method of HNO₃ + H₂O₂ (National Standard of China, GB 17378.6-2007). Sample solutions were analyzed for Cu, Cr, and Cd, using Graphite Furnace Atomic Absorption Spectrophotometer (GF-AAS).
Granulometry was analyzed using a laser particle size analyzer (Mastersizer 2000, Malvern) and pH was performed by Vario pH meter (SMCH-2V00-001V, German).

A dentist recorded each individual’s number of amalgam surfaces after visual inspection and x-rays. Age, sex, weight, and symptom severity were gathered from routinely administered surveys and medical professional consultations. Mercury levels were measured from a sample provided by consenting participants at an appointment. The urine samples were sent by priority shipping to Doctor’s Data, Inc. (St. Charles, IL). On receipt, aliquots of each creatinine sample were made and the remaining sample was acidified to preserve mercury. Creatinine measurement was performed using a modified Jaffe method on a Beckman Coulter AU680. Samples were prepared for elemental testing based on creatinine level and measured using ICP-MS (Perkin Elmer DRCII) [38 (link)]. Urine mercury concentrations are reported as μg/g-creatinine to reduce error introduced by variation in sample volume. Urine samples were used as they are a valid measure of body burden from long term constant exposure to elemental mercury [39 (link)].

Mineral elements were measured, as described by Rui et al. [21 ]. Briefly, rice plants with different treatments were harvested, thoroughly washed, and dried at 65 °C to prepare 0.2 g dry rice samples (roots and aboveground) for the determination of mineral elements. Dried rice samples were ground into powder and thoroughly digested in a mixed solution of nitric acid: hydrofluoric acid (1:2) using a microwave digestion system (XT-9916, XTrust, Xiamen, China). The digests were diluted to 10 mL with ultrapure water and assayed by ICP-MS (DRCII, PerkinElmer, and Norwalk, CT, USA).