Stimulation of 2-methylisoborneol (MIB) production by actinomycetes after cyclic chlorination in drinking water distribution systems

Our plain-English summary of Stimulation of 2-methylisoborneol (MIB) production by actinomycetes after cyclic chlorination in drinking water distribution systems, by M. Abbaszadegan, M. Yi, A. Alum (Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering, 2015).

The study

• Authors: M. Abbaszadegan, M. Yi, A. Alum
• Journal: Journal of Environmental Science and Health. Part A, Toxic/hazardous Substances & Environmental Engineering
• Published: 2015;50(4):365-71
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The impact of fluctuation in chlorine residual on actinomycetes and the production of 2-methylisoborneol (MIB) were studied in cast-iron and PVC model distribution systems. Actinomycetes were spiked in each system and continued operation for a 12-day non-chlorine experiment, resulting in no changes in actinomycetes and MIB concentrations. Three cyclic chlorination events were performed and chlorine residuals were maintained as follows: 1.0 mg L(-1) for 24 h, 0 mg L(-1) for 48 h, 0.5 mg L(-1) for 48 h, 0 mg L(-1) for 48 h and 2 mg L(-1) for 24 h. After each chlorination event, 2 -3 log decrease in actinomycetes was noted in both systems. However, within 48 h at 0 mg L(-1) chlorine, the actinomycetes recovered to the pre-chlorination levels. On the contrary, MIB concentration in both systems remained un-impacted after the first cycle and increased by fourfold (< 5 to > 20 mg L(-1)) after the second cycle, which lasted through the third cycle despite the fact that actinomycetes numbers fluctuated 2-3 logs during this time period. For obtaining biofilm samples from field, water meters were collected from municipality drinking water distribution systems located in central Arizona. The actinomycetes concentration in asbestos cement pipe and cast iron pipe averaged 3.1 × 10(3) and 1.9 × 10(4) CFU cm(-2), respectively. The study shows that production of MIB is associated with changes in chlorine residual in the systems. This is the first report of cyclic chlorine shock as a stimulus for MIB production by actinomycetes in drinking water distribution system's ecology.

In plain English

This laboratory and field study was about taste and odor in drinking water, not asbestos-related disease. Asbestos appears only as a pipe material in the field sampling. The authors added Streptomyces griseus, an actinomycete known to produce the camphor-smelling compound MIB, to two 50-litre model pipe loops, one cast iron and one PVC. They then ran three chlorination cycles at 1.0, 0.5 and 2.0 mg per litre of free chlorine. After each cycle, culturable actinomycetes fell by about 2 log10 and then recovered. MIB did not rise after the first cycle. At the start of the second cycle it rose from 2.5 to 22.7 ng/L in the cast-iron loop and from 2.3 to 20.5 ng/L in the PVC loop, and stayed raised through the third cycle. In biofilm from water meters in a central Arizona system, actinomycetes averaged 3.1 × 10³ colony-forming units per square centimetre at meters on asbestos cement pipe and 1.9 × 10⁴ at meters on cast-iron pipe. The authors reported no significant difference between the two. They concluded that the second chlorination cycle acted as a stimulant for MIB production.

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 experiment in model drinking water distribution systems, plus field sampling of biofilm from municipal water meters
• Who was studied: Two 50-L model pipe loops (cast iron and PVC) spiked with Streptomyces griseus subspecies griseus (ATCC 3343). Field: biofilm from brass water meters at 10 locations in a central Arizona municipal system, with pipes 34 to 37 years old. Locations 1 to 8 were on asbestos cement pipe and locations 9 and 10 on cast-iron pipe.
• Exposure: Cyclic chlorination: free chlorine held at 1.0, 0.5 and 2.0 mg/L for 24, 48 and 24 h in the 1st, 2nd and 3rd cycles, each followed by chlorine depletion. Pipe material (asbestos cement vs cast iron) in the field samples.
• Main results:
  • With no chlorine for 12 days, neither model system showed significant changes in actinomycetes or MIB.
  • After each chlorination cycle, culturable actinomycetes in the model systems decreased by approximately 2 log10, then increased again as chlorine was depleted.
  • In both model systems, actinomycetes did not produce MIB after the first chlorine shock (1.0 mg/L).
  • At the start of the second chlorination cycle, MIB rose from 2.5 to 22.7 ng/L in the cast-iron system and from 2.3 to 20.5 ng/L in the PVC system. The levels persisted through the third cycle.
  • The third chlorination cycle (2.0 mg/L) had no significant impact on MIB concentration in either system.
  • In the field biofilm samples, actinomycetes averaged 3.1 × 10³ CFU per square centimetre at asbestos cement pipe locations and 1.9 × 10⁴ CFU per square centimetre at cast-iron pipe locations. The authors reported no significant difference between pipe types and no direct correlation with pipe age (covariance -1153.6).
• The authors' conclusion: The authors concluded that a second chlorination cycle acted as a stimulant for MIB production by actinomycetes. They recommended maintaining a steady chlorine residual in distribution systems.
• Limitations the authors state:
  • The authors stated that results from the 10 field locations may not be directly comparable, because locations 1 to 8 were on asbestos cement pipe and locations 9 and 10 on cast-iron pipe.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement.

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