Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems

Our plain-English summary of Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems, by S.S. Andra, K.C. Makris, G. Botsaris, et al (The Science of the Total Environment, 2014).

The study

• Authors: S.S. Andra, K.C. Makris, G. Botsaris, P. Charisiadis, H. Kalyvas, C.N. Costa
• Journal: The Science of the Total Environment
• Published: 2014;472:1145-51
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Changes in disinfectant type could trigger a cascade of reactions releasing pipe-anchored metals/metalloids into finished water. However, the effect of pre-formed disinfection by-products on the release of sorbed contaminants (arsenic-As in particular) from drinking water distribution system pipe scales remains unexplored. A bench-scale study using a factorial experimental design was performed to evaluate the independent and interaction effects of trihalomethanes (TTHM) and haloacetic acids (HAA) on arsenic (As) release from either scales-only or scale-biofilm conglomerates (SBC) both anchored on asbestos/cement pipe coupons. A model biofilm (Pseudomonas aeruginosa) was allowed to grow on select pipe coupons prior experimentation. Either TTHM or HAA individual dosing did not promote As release from either scales only or SBC, detecting <6 μg AsL(-1) in finished water. In the case of scales-only coupons, the combination of the highest spike level of TTHM and HAA significantly (p<0.001) increased dissolved and total As concentrations to levels up to 16 and 95 μg L(-1), respectively. Similar treatments in the presence of biofilm (SBC) resulted in significant (p<0.001) increase in dissolved and total recoverable As up to 20 and 47 μg L(-1), respectively, exceeding the regulatory As limit. Whether or not, our laboratory-based results truly represent mechanisms operating in disinfected finished water in pipe networks remains to be investigated in the field.

Copyright © 2013 Elsevier B.V. All rights reserved.

In plain English

This was a laboratory experiment, not a study of people. The authors cut small coupons from previously leaking asbestos–cement pipes disconnected from the Nicosia, Cyprus system. They coated them with a synthetic iron–arsenic scale and grew Pseudomonas aeruginosa biofilm on some. The coupons sat in tap water for 24 hours (two replicates per treatment) with disinfection by-products added on top of those already present: trihalomethanes (TTHM) alone, haloacetic acids (HAA) alone, or TTHM up to 100 μg per litre plus HAA at 10 or 60 μg per litre. The study measured arsenic and iron in the water, not asbestos. TTHM or HAA alone produced small, not statistically significant increases in arsenic (up to 6 μg per litre). With the highest combined doses, dissolved and total arsenic rose to 16 and 95 μg per litre on scale-only coupons (controls 0.1 and 0.8). On biofilm coupons they rose to 20 and 47 μg per litre (controls 0.1 and 1.5); both increases were statistically significant. Total arsenic was significantly correlated with iron in the water. The authors called their results preliminary, to be treated with caution.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory bench-scale factorial experiment testing the separate and combined effects of two groups of disinfection by-products on arsenic release from pipe pieces
• Who was studied: No people were studied. The test material was coupons (about 4 by 3 by 1.5 cm) cut from previously leaking asbestos–cement (A/C) water pipe segments disconnected from the Nicosia, Cyprus distribution system. Each coupon carried a synthetic iron–arsenic scale, either alone ('scales-only') or with a grown Pseudomonas aeruginosa biofilm ('scale-biofilm conglomerates', SBC). There were 2 replicates per treatment.
• Exposure: Coupons sat for 24 hours in 200 mL of tap water with added trihalomethanes (TTHM: four species) and/or haloacetic acids (HAA: nine species). There were four treatments: TTHM alone, HAA alone, and TTHM at varying levels combined with HAA fixed at 10 or 60 μg per litre. Additions ranged from 0 to 100 μg per litre and were made on top of the by-products already present in the tap water. The asbestos–cement pipe served only as the surface for the scales; the outcomes measured were arsenic and iron in the water.
• Main results:
  • Adding TTHM alone or HAA alone gave small increases in total and dissolved arsenic (up to 6 μg per litre) that were not statistically significant, for both scales-only and biofilm (SBC) coupons.
  • Scales-only coupons: the highest combined TTHM and HAA doses significantly (p less than 0.001) raised dissolved arsenic to up to 16 μg per litre and total arsenic to up to 95 μg per litre, compared with 0.1 and 0.8 μg per litre in controls.
  • Biofilm (SBC) coupons: the same treatments significantly (p less than 0.001) raised dissolved arsenic to up to 20 μg per litre and total recoverable arsenic to up to 47 μg per litre, compared with 0.1 and 1.5 μg per litre in controls.
  • The biofilm did not significantly change dissolved arsenic compared with scales-only coupons. With 60 μg per litre HAA, adding 10 and 100 μg per litre TTHM gave significantly higher total arsenic on scales-only coupons than on biofilm coupons (33 vs. 18 μg per litre, and 95 vs. 47 μg per litre).
  • Total recoverable arsenic was significantly (p less than 0.001) correlated with total iron in the water.
  • In runs with both TTHM and HAA, the TTHM remaining at the end was negatively correlated with released arsenic (p = 0.03) and with released iron (p = 0.02).
  • Even with the lower HAA level (10 μg per litre), arsenic release exceeded the 10 μg per litre regulatory limit when TTHM was at 100 μg per litre.
• The authors' conclusion: The authors concluded that their results are preliminary and should be treated with caution, and that whether these laboratory findings reflect what happens in real disinfected pipe networks remains to be investigated.
• Limitations the authors state:
  • Tap water was used to simulate field conditions; a simpler matrix (deionized water) may have allowed better control of experimental conditions.
  • Whether disinfection by-products promote arsenic release, beyond the authors' speculated mechanisms, remains unanswered.
  • It is unclear why TTHM and HAA both had to be present at high concentrations to mobilize arsenic.
  • Haloacetic acid concentrations were not measured, because of analytical complexity and the lack of an in-house protocol.
  • A possible role of microbial activity was not the main focus of the study.
  • Whether the laboratory results represent what happens in real disinfected pipe networks remains to be investigated in the field.

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