Engineering and operating approaches for controlling asbestos fibers in drinking water

Our plain-English summary of Engineering and operating approaches for controlling asbestos fibers in drinking water, by G.S. Logsdon (Environmental Health Perspectives, 1983).

The study

• Author: G.S. Logsdon
• Journal: Environmental Health Perspectives
• Published: 1983;53:169-76
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Techniques are available to minimize the concentration of asbestos fibers in drinking water. Filtration research conducted at locations on Lake Superior and in the Cascade Mountains in Washington has shown that amphibole and chrysotile fibers can be removed by granular media filtration. Removal percentages can exceed 99% when the raw water is coagulated properly and the filtered water turbidity is 0.10 ntu (nephelometric turbidity units) or lower. Filtered water fiber counts below detectable limits of 0.1 to 0.01 X 10(6) fibers/L can be attained. A study by the Metropolitan Water District of Southern California showed that when raw water chrysotile counts ranged from 200 X 10(6) fibers/L to 2000 X 10(6) fibers/L, filtered water fiber counts frequently exceeded 1 X 10(6) fibers/L. Even so, striving to attain a filtered water turbidity of 0.1 ntu resulted in improved fiber removal. Pilot scale and distribution system research projects have shown that asbestos cement (AC) pipes can be protected from dissolution and leaching effects that can result in release of asbestos fibers into drinking water. Suggested techniques include modifying low pH, low alkalinity waters so they are not aggressive; coating the pipe wall with a chemical precipitate; and applying a cement mortar lining to the pipe wall. Operation and maintenance practices related to the distribution system, when AC water mains are in service, can influence the fiber count in tapwater. Main flushing can stir up sediment that accumulates in low-flow and dead-end areas, raising the fiber count. If mains are tapped and the cuttings are not flushed away through the tapping machine, but are instead permitted to fall into the water main, the fiber count can be raised.

In plain English

This paper, by an author at the U.S. Environmental Protection Agency's Drinking Water Research Division, summarized engineering research on limiting asbestos fibers in drinking water. It reviewed earlier projects and was not a health study. In the filtration work reviewed, plants at Silver Bay and Two Harbors on Lake Superior reduced amphibole fiber counts by 99% and more. Pilot projects in Washington's Cascade Mountains removed more than 99% of chrysotile fibers. A Southern California study by other researchers found filtered-water chrysotile counts often of 1 to 50 million fibers per liter, even when turbidity was near or below 0.10 ntu. Optimized operation lowered the median counts. For asbestos cement pipe, the studies reviewed found that soft, low pH water had deteriorated pipe and that coatings such as zinc or calcium carbonate could protect it. At Weston, results suggested that scraping or pigging greatly increased fiber counts. The effect of cement mortar lining could not be firmly judged because fiber counting was imprecise at low levels. The author concluded that utility operating practices can influence fiber levels in drinking water.

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: Review summarizing engineering research (pilot plant, treatment plant, laboratory tank and field distribution system studies) on asbestos fiber removal and asbestos cement pipe protection
• Who was studied: Water filtration plants and pilot plants on Lake Superior in Minnesota (Duluth, Two Harbors, Beaver Bay, Silver Bay), in the Cascade Mountains of Washington (Seattle's South Fork Tolt Reservoir, Everett) and three Metropolitan Water District of Southern California plants. Also asbestos cement pipe studies at the EPA laboratory in Cincinnati, Greenwood, SC, Bellevue, WA, Weston, WI and Ashland, MA, roughly 1974 to 1981.
• Exposure: Amphibole and chrysotile asbestos fibers in raw (source) water, and asbestos fibers released from asbestos cement (AC) pipe carrying aggressive (soft, low pH, low alkalinity) water
• Main results:
  • Filtration plants at Silver Bay and Two Harbors on Lake Superior achieved amphibole fiber count reductions of 99% and more. Filtered water at the Lakewood plant in Duluth generally contained fewer than 0.10 x 10^6 fibers/L.
  • Pilot plant projects in the Cascade Mountains (Seattle Tolt and Everett) demonstrated chrysotile fiber removal exceeding 99%.
  • At three Metropolitan Water District of Southern California plants, raw water counts were generally 200 x 10^6 to 2000 x 10^6 fibers/L. A report by McGuire et al. found filtered-water chrysotile concentrations frequently from 1 x 10^6 to 50 x 10^6 fibers/L, even with turbidity near or below 0.10 ntu.
  • At the Weymouth, Diemer and Mills plants, the median filtered-water fiber count under optimized operation was considerably below the median under standard operation. The author stated that the lower counts were a result of the optimized operation.
  • Data from the Seattle study showed that fiber counts can increase sharply with modest increases in turbidity.
  • Field evaluations of AC pipe at 10 locations found deteriorated AC pipe in four systems with soft, low pH water.
  • At Greenwood, SC, zinc orthophosphate was fed at an average of 0.3 mg/L. Asbestos fibers in the water decreased substantially and zinc coatings formed on test pipe sections.
  • In the Bellevue tank tests, the zinc chloride strategies (tanks T5 and T6) were the most effective in controlling attack on AC pipe.
  • In hardness tests, coupons exposed to Tolt water and used pipe of unknown history were softer than new pipe. Average Shore D hardness was 65.5 and 70.5, compared with 80.0 for new pipe. Differences between means were significant at the 0.05 level.
  • In used AC pipe from Weston, calcium was depleted near the inner wall to depths of 2.1 mm to 6.5 mm. Pipe from four other cities showed losses to depths of 0.8 mm to 3.6 mm.
  • At Weston, results of fiber analyses suggested that scraping or pigging AC mains, although it can remove the softened part of the pipe wall, greatly increases the fiber count of water carried in the pipes.
  • In one Wisconsin system, flushing an AC main for 1 minute produced about 10 billion fibers/L in a fire hydrant sample. Undisturbed household tap samples contained about 5-7 million fibers/L.
• The authors' conclusion: The author concluded that diatomaceous earth and granular media filters can remove asbestos fibers from source waters, and that a filtered-water turbidity of 0.10 ntu or lower is a goal if fiber removal is intended. The author also concluded that coatings may protect AC pipe, and that utility operating practices such as tapping and flushing can influence asbestos fiber concentrations in drinking water.
• Limitations the authors state:
  • Firm conclusions about cement mortar lining as a barrier to fibers were not possible because asbestos counting is imprecise at low fiber concentrations.
  • Additional research at plants with very high raw water fiber counts is needed to explain the Southern California results and the apparent shortcomings of the 0.10 ntu goal.
  • Further study may be needed before definitive recommendations on main flushing can be made.
  • The hardness testing data were described as preliminary.

Topics

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

Related studies

• Asbestos in drinking water: a status report — J.A. Cotruvo (1983)
• Use of quantitative analysis of urine to assess exposure to asbestos fibers in drinking water in the Puget Sound region — E.S. Boatman, T. Merrill, et al. (1983)
• Epidemiology study of the use of asbestos-cement pipe for the distribution of drinking water in Escambia County, Florida — J.R. Millette, G.F. Craun, et al. (1983)
• Cancer incidence following exposure to drinking water with asbestos leachate — H.L. Howe, P.E. Wolfgang, et al. (1989)
• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)
• Asbestos in drinking water and cancer — K.D. MacRae (1988)

Browse more research in Environmental Health Perspectives, or return to medical research.