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Boron Exposure Assessment of Desalinated Seawater on an Island in China

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This study monitored boron in finished and tap water from desalinated seawater, reservoir and mixed sources on a Chinese island for one year, measured total boron intake by a three-day duplicate-diet method in 32 families and measured urinary boron in 199 residents. Desalinated water exceeded the then-current Chinese limit of 0.5 mg/L, while mixed water was lower. Diet supplied most of the boron intake, and total intake was well below the WHO tolerable daily intake used by the authors.

Key numbers

  • Boron in finished water: desalinated 0.68 to 1.46 mg/L (n = 51), reservoir 0.30 to 0.39 mg/L (n = 39), mixed 0.32 to 0.43 mg/L (n = 7); tap water: desalinated 0.62 to 1.26 mg/L (n = 60), reservoir 0.20 to 0.50 mg/L (n = 64), mixed 0.20 to 0.79 mg/L (n = 14) (Table 1, p. 6).
  • Boron intake (32 family representatives): water 0.113 ± 0.127 mg/d, diet 1.562 ± 0.927 mg/d, total 1.674 ± 0.939 mg/d (Table 3, p. 7).
  • Total boron exposure: 0.030 ± 0.012 mg/kg bw per day versus a TDI of 0.17 mg/kg bw per day (Table 6, p. 8).
  • Urinary boron, creatinine-corrected (morning urine): average 1.851 mg/g creatinine (n = 199); median males 1.569 (n = 93) and females 2.148 mg/g creatinine (n = 106), P = 0.018 (Table 4, p. 8).
  • Hazard quotients for water: maximum 0.24 (desalinated finished water), minimum 0.03 (Table 5, p. 8), using an RfD of 0.2 mg/kg per day (Section 2.4.1, p. 5).
  • Food detection limit (ICP-MS, GB/T 21918-2008): 0.20 mg/kg (Section 2.3.2, p. 5).
  • Background limits stated: WHO guideline value revised from 0.5 to 2.4 mg/L in 2011; China GB 5749-2006 limit 0.5 mg/L, revised to 1.0 mg/L from 2023; Canada maximum acceptable concentration 2 mg/L (Background, p. 2; Discussion, p. 9).

Methods (brief)

Water from 5 finished and 13 tap sites was sampled monthly from May 2015 to April 2016 (235 samples) and analyzed by azomethine-H spectrophotometry (GB/T 5750). In May 2016, one representative in each of 32 families collected duplicate portions of all meals for three days; food was microwave-digested and analyzed by ICP-MS with yttrium internal standard. Morning urine from all participants was analyzed by ICP-MS and corrected for creatinine. Water risk was assessed with the US EPA hazard-quotient model.

Evidence fitness

Supports drinking-water boron concentrations by source, duplicate-diet total intake and urinary boron in an island population using desalinated water, and shows that blending with reservoir water lowers boron. It does not support health outcomes or concentrations in individual foods.

Limitations

Small duplicate-diet subsample (32 families) with one person representing each family; single morning urine rather than 24-hour collection; water and diet sampling were a year apart. Funded by a national public welfare research project; no conflicts declared.

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