Final Report Summary - STACS (Stability of sorbed arsenic by pipe scales and biofilms in drinking water distribution systems)
Background
Low-level release of toxic trace metalloids and metals, like arsenic (As) and lead (Pb) in urban drinking-water distribution systems (UDWDS) represents an important source of unintentional exposures for tap water consumers. Of considerable concern in the European Union (EU)-27 is the increasing in frequency cases of household water quality deterioration in aging UDWDS in the transit (between water treatment plant and kitchen tap). Nearly 10 years ago, a prime example of this exposure scenario was the widespread spike in children blood Pb levels in Washington District of Columbia due to episodic Pb release from water pipes resulted from a change in disinfectant type triggering destabilisation of Pb pipe scales. It appears plausible that other co-occurring contaminants may be found on drinking-water pipes, like As, particularly in endemic low-level As contaminated raw water supplies around the EU. Despite the fact that aging of water distribution pipes could significantly contribute to water quality deficiencies, replacement of aging pipes in each European city represents an extremely cost-ineffective intervention, calling for smart and sustainable control options.
The challenges
During processes that last for decades, pipe scales and corrosion products gradually builds on water pipe surfaces often acting as sinks for various toxic trace contaminants in drinking-water. These usually end up, unintentionally, finding their way into water supply. Low-level, As concentrations in potable water supplies may be historically accumulating in pipe solids and scales within UDWDS as a result of adsorption / precipitation reactions on pipe surfaces. Such As pipe solids may be considered stable over time, due to their low solubility product, but limited knowledge exists on various environmental factors that could induce episodic and non-periodic pipe scale destabilisation phenomena. It is likely that current water monitoring and surveillance schemes of finished water quality will likely miss such metal release events, if they arise asymmetrically in time and space. This situation may be perplexed because of the large variability in water treatment technologies and pipe network characteristics observed for cities in the EU-27. We believe that even subtle changes in historically-equilibrated UDWDS would have to be monitored in the context of possible destabilisation and contaminant release events. Another challenge relates to the unpredicted and pulsed nature of an episodic release event for such harboured contaminants from pipe scales and biofilm conglomerates (SBC) into water. Our STACS project tested the hypothesis that subtle changes in finished water chemistry in aging UDWDS could have major impact on the stability of lodged contaminants, resulting in their spontaneous release from SBC complexes to tap water. Arsenic as the study case was extensively studied, because of its extremely high carcinogenicity upon oral ingestion. Understanding the factors and mechanisms behind As release from SBC may serve as a control measure to minimise occurrence of episodic contaminant release incidences in potable water supplies of the EU cities.
STACS project objectives
STACS implemented the following objectives:
i) it characterised the physicochemical properties of studied water samples, pipe SBC obtained from the UDWDS in Nicosia, Cyprus;
ii) it studied the water quality variables prevailing in UDWDS that have a significant influence on As destabilisation and release from pipe scales / SBC into water;
iii) it evaluated the role of disinfection by-products controlling As fate and release from pipe scales;
iv) it identified co-occurring inorganic contaminant classes in potable waters and related with their co-release behaviour from pipe scales / SBC; and
v) it evaluated low-level As exposures from drinking-water and their association with diabetes mellitus incidences in a Cypriot community.
Analysis of scientific literature about drinking-water quality deterioration in water distribution pipes
STACS personnel studied the in-depth relationships between pipe scales, biofilms and tap water chemistry in the context of contaminant release in UDWDS. This effort resulted in publishing a critical review, being one of the main deliverables (Makris et al., 2013). Important synergistic SBC effects on finished water quality were identified as:
i) those promoting chemical release from pipe scales due to biofilm-induced alterations at the pipe surface / water interface;
ii) the synergistic SBC action on promoting increased release rates of pathogens or toxic chemicals into water; and
iii) the microbially-enhanced corrosive phenomena on pipe scales and their constituents.
Experimental methodology
One of the key aspirations of STACS was to understand the independent and interaction effects of several water quality variables on the fate of accumulated As in pipe scales and SBC. Simulated UDWDS conditions in a laboratory set-up were prepared for the proposed studies. We prepared asbestos / cement (A / C) coupons laden with As from field-collected A / C pipes that were upheaved due to leaking incidences. Certain A / C pipe coupons were used to grow a model microbe typically detected in a UDWDS biofilm community (Pseudomonas species). A validated protocol was developed for optimised distribution of pipe scales and biofilm on each A / C pipe coupon. Three different experimental scenarios were tested:
i) synthesised iron (Fe)-As solids representing the major form of As in pipe scales;
ii) A / C pipe coupons containing synthesised Fe-As scales; and
iii) A / C pipe coupons containing synthesised Fe-As scales with inoculated Pseudomonas aeruginosa biofilm. Validated analytical methods were used for analysing:
i) inorganics analysis with an inductively coupled plasma mass spectrometer (e.g. As and other elements);
(ii) Fe2+ and Fe3+ with a spectrophotometer; and
iii) disinfection by-products using a gas chromatograph coupled with triple quadruple mass spectrometer.
Screening for influential water chemistry parameters on pipe scales destabilisation and As release to water
The Plackett-Burman Design (PBD) tested 10 water quality variables with minimal number of experimental runs: pH, alkalinity, chloride, free chlorine, sulfate, orthophosphate, trihalomethanes (TTHM) (viz. bromodichloromethane, chloroform, bromofrom, dibromochloromethane), haloacetic acids (HAA) (viz., bromoacetic acid, bromochloroacetic acid, bromodichloroacetic acid, chloroacetic acid, dibromochloroacetic acid, dibromoacetic acid, dichloroacetic acid, tribromoacetic acid, and trichloroacetic acid), hydroxylamine, and a mixture of nine common nitrosamines. Main and interaction effects of the four significant variables (TTHM, HAA, sulfate, and orthophosphate) as identified in the PBD experiment were further evaluated using a central composite design (CCD). A noticeable synergistic interaction effect between TTHM and HAA was observed, resulting in proportional increase in total soluble and dissolved As fractions in tap water as observed in both pipe scales and SBC treatments (Andra et al., 2013a; Manuscript submitted).
Effect of disinfection by-products on As release
A factorial experimental design assessed the effect of spiking TTHM and HAA into water up to 100 and 60 µg L-1, respectively. Interestingly, addition of TTHM or HAA alone did not promote As release to levels above the regulatory limit of 10 µg L-1, while it was well exceeded in treatments employing both TTHM and HAA. We speculated that As release under the experimental conditions was controlled by the dissolution of iron-based pipe scale, which in turn was influenced by the presence of both TTHM and HAA concentrations. Even in a conservative scenario with lower HAA concentrations (viz. 10 µg L-1), As release exceeded its current 10 µg L-1 regulatory limit in the presence of TTHM at 100 µg L-1. In addition to the elevated health risk posed by TTHM / HAA themselves, water board authorities would have to monitor possible leaching of sorbed metals or contaminants by pipe scales into finished water, whenever increased DBP formation is observed in the respective district metered areas (Andra et al., 2013a; Manuscript submitted).
Profiling of potable water samples for co-occurring contaminant mixtures
STACS findings may be used towards understanding not only release of As but also co-occurring contaminants in pipe scales with similar chemical properties. Because of the inherent difficulty collecting pipe scales from UDWDS, profiling patterns of trace elements in finished water could be indicative of their load on pipe scales and corrosion products (Andra et al., 2013b; Manuscript submitted).
Low level exposures to As and health risk assessment
From a human health assessment perspective, STACS project with the help of epidemiologists identified weak associations between:
i) low-level exposures to As from drinking water ingestion and diabetes prevalence in a Cypriot community (Makris et al., 2012); and
ii) the relationship between a couple biomarkers of As exposure and type 2 diabetes incidences from a literature review conducted globally (Andra et al., 2013).
Socioeconomic and regulatory impact
The STACS project findings have practical implications for water boards and regulatory agencies serving historically low-level As-contaminated areas. Implementation of the revised As drinking water rule 10 years ago lowered the maximum permissible limit of As from 50 to 10 µg L-1, including rural and small communities (< 2 000 people). Assuming historic accumulation of low level As levels on the internal surfaces of pipe scales and/or SBC, despite meeting the 10 µg As L-1 regulatory limits in As-impacted areas, may have resulted in a distinct As concentration gradient at the pipe surface-flowing water interface and the water. If no changes in the UDWDS water quality are foreseen, historically dormant As will remain tenaciously sorbed by pipe scales. However, the tendency to increase chlorination levels during summer in Mediterranean countries could create the circumstances of producing high concentrations of disinfection by-products. Concurrently, chemisorbed As by pipes may react with formed TTHM / HAA disrupting the pseudo-equilibrium As state, and thus, initiating As release phenomena. This scenario may be most probable in certain areas within the same UDWDS characterised by higher risk formation potential for disinfection by-products, suggesting that such vulnerable areas needs most of the attention from respective water boards. This will contribute to continue safeguarding the quality of potable water in the EU cities against unintentional ingestion exposures to episodic incidences of contaminant release events into tap water.
Contact: Dr Konstantinos C. Makris, Assistant Professor of Environmental Health, Cyprus International Institute for Environmental and Public Health in association with Harvard School of Public Health, Cyprus University of Technology. Irenes 95, Limassol 3041, Cyprus. Telephone: +35-725-002398. Email: konstantinos.makris@cut.ac.cy
List of websites: http://www.cut.ac.cy/waterandhealth/(si apre in una nuova finestra)
Low-level release of toxic trace metalloids and metals, like arsenic (As) and lead (Pb) in urban drinking-water distribution systems (UDWDS) represents an important source of unintentional exposures for tap water consumers. Of considerable concern in the European Union (EU)-27 is the increasing in frequency cases of household water quality deterioration in aging UDWDS in the transit (between water treatment plant and kitchen tap). Nearly 10 years ago, a prime example of this exposure scenario was the widespread spike in children blood Pb levels in Washington District of Columbia due to episodic Pb release from water pipes resulted from a change in disinfectant type triggering destabilisation of Pb pipe scales. It appears plausible that other co-occurring contaminants may be found on drinking-water pipes, like As, particularly in endemic low-level As contaminated raw water supplies around the EU. Despite the fact that aging of water distribution pipes could significantly contribute to water quality deficiencies, replacement of aging pipes in each European city represents an extremely cost-ineffective intervention, calling for smart and sustainable control options.
The challenges
During processes that last for decades, pipe scales and corrosion products gradually builds on water pipe surfaces often acting as sinks for various toxic trace contaminants in drinking-water. These usually end up, unintentionally, finding their way into water supply. Low-level, As concentrations in potable water supplies may be historically accumulating in pipe solids and scales within UDWDS as a result of adsorption / precipitation reactions on pipe surfaces. Such As pipe solids may be considered stable over time, due to their low solubility product, but limited knowledge exists on various environmental factors that could induce episodic and non-periodic pipe scale destabilisation phenomena. It is likely that current water monitoring and surveillance schemes of finished water quality will likely miss such metal release events, if they arise asymmetrically in time and space. This situation may be perplexed because of the large variability in water treatment technologies and pipe network characteristics observed for cities in the EU-27. We believe that even subtle changes in historically-equilibrated UDWDS would have to be monitored in the context of possible destabilisation and contaminant release events. Another challenge relates to the unpredicted and pulsed nature of an episodic release event for such harboured contaminants from pipe scales and biofilm conglomerates (SBC) into water. Our STACS project tested the hypothesis that subtle changes in finished water chemistry in aging UDWDS could have major impact on the stability of lodged contaminants, resulting in their spontaneous release from SBC complexes to tap water. Arsenic as the study case was extensively studied, because of its extremely high carcinogenicity upon oral ingestion. Understanding the factors and mechanisms behind As release from SBC may serve as a control measure to minimise occurrence of episodic contaminant release incidences in potable water supplies of the EU cities.
STACS project objectives
STACS implemented the following objectives:
i) it characterised the physicochemical properties of studied water samples, pipe SBC obtained from the UDWDS in Nicosia, Cyprus;
ii) it studied the water quality variables prevailing in UDWDS that have a significant influence on As destabilisation and release from pipe scales / SBC into water;
iii) it evaluated the role of disinfection by-products controlling As fate and release from pipe scales;
iv) it identified co-occurring inorganic contaminant classes in potable waters and related with their co-release behaviour from pipe scales / SBC; and
v) it evaluated low-level As exposures from drinking-water and their association with diabetes mellitus incidences in a Cypriot community.
Analysis of scientific literature about drinking-water quality deterioration in water distribution pipes
STACS personnel studied the in-depth relationships between pipe scales, biofilms and tap water chemistry in the context of contaminant release in UDWDS. This effort resulted in publishing a critical review, being one of the main deliverables (Makris et al., 2013). Important synergistic SBC effects on finished water quality were identified as:
i) those promoting chemical release from pipe scales due to biofilm-induced alterations at the pipe surface / water interface;
ii) the synergistic SBC action on promoting increased release rates of pathogens or toxic chemicals into water; and
iii) the microbially-enhanced corrosive phenomena on pipe scales and their constituents.
Experimental methodology
One of the key aspirations of STACS was to understand the independent and interaction effects of several water quality variables on the fate of accumulated As in pipe scales and SBC. Simulated UDWDS conditions in a laboratory set-up were prepared for the proposed studies. We prepared asbestos / cement (A / C) coupons laden with As from field-collected A / C pipes that were upheaved due to leaking incidences. Certain A / C pipe coupons were used to grow a model microbe typically detected in a UDWDS biofilm community (Pseudomonas species). A validated protocol was developed for optimised distribution of pipe scales and biofilm on each A / C pipe coupon. Three different experimental scenarios were tested:
i) synthesised iron (Fe)-As solids representing the major form of As in pipe scales;
ii) A / C pipe coupons containing synthesised Fe-As scales; and
iii) A / C pipe coupons containing synthesised Fe-As scales with inoculated Pseudomonas aeruginosa biofilm. Validated analytical methods were used for analysing:
i) inorganics analysis with an inductively coupled plasma mass spectrometer (e.g. As and other elements);
(ii) Fe2+ and Fe3+ with a spectrophotometer; and
iii) disinfection by-products using a gas chromatograph coupled with triple quadruple mass spectrometer.
Screening for influential water chemistry parameters on pipe scales destabilisation and As release to water
The Plackett-Burman Design (PBD) tested 10 water quality variables with minimal number of experimental runs: pH, alkalinity, chloride, free chlorine, sulfate, orthophosphate, trihalomethanes (TTHM) (viz. bromodichloromethane, chloroform, bromofrom, dibromochloromethane), haloacetic acids (HAA) (viz., bromoacetic acid, bromochloroacetic acid, bromodichloroacetic acid, chloroacetic acid, dibromochloroacetic acid, dibromoacetic acid, dichloroacetic acid, tribromoacetic acid, and trichloroacetic acid), hydroxylamine, and a mixture of nine common nitrosamines. Main and interaction effects of the four significant variables (TTHM, HAA, sulfate, and orthophosphate) as identified in the PBD experiment were further evaluated using a central composite design (CCD). A noticeable synergistic interaction effect between TTHM and HAA was observed, resulting in proportional increase in total soluble and dissolved As fractions in tap water as observed in both pipe scales and SBC treatments (Andra et al., 2013a; Manuscript submitted).
Effect of disinfection by-products on As release
A factorial experimental design assessed the effect of spiking TTHM and HAA into water up to 100 and 60 µg L-1, respectively. Interestingly, addition of TTHM or HAA alone did not promote As release to levels above the regulatory limit of 10 µg L-1, while it was well exceeded in treatments employing both TTHM and HAA. We speculated that As release under the experimental conditions was controlled by the dissolution of iron-based pipe scale, which in turn was influenced by the presence of both TTHM and HAA concentrations. Even in a conservative scenario with lower HAA concentrations (viz. 10 µg L-1), As release exceeded its current 10 µg L-1 regulatory limit in the presence of TTHM at 100 µg L-1. In addition to the elevated health risk posed by TTHM / HAA themselves, water board authorities would have to monitor possible leaching of sorbed metals or contaminants by pipe scales into finished water, whenever increased DBP formation is observed in the respective district metered areas (Andra et al., 2013a; Manuscript submitted).
Profiling of potable water samples for co-occurring contaminant mixtures
STACS findings may be used towards understanding not only release of As but also co-occurring contaminants in pipe scales with similar chemical properties. Because of the inherent difficulty collecting pipe scales from UDWDS, profiling patterns of trace elements in finished water could be indicative of their load on pipe scales and corrosion products (Andra et al., 2013b; Manuscript submitted).
Low level exposures to As and health risk assessment
From a human health assessment perspective, STACS project with the help of epidemiologists identified weak associations between:
i) low-level exposures to As from drinking water ingestion and diabetes prevalence in a Cypriot community (Makris et al., 2012); and
ii) the relationship between a couple biomarkers of As exposure and type 2 diabetes incidences from a literature review conducted globally (Andra et al., 2013).
Socioeconomic and regulatory impact
The STACS project findings have practical implications for water boards and regulatory agencies serving historically low-level As-contaminated areas. Implementation of the revised As drinking water rule 10 years ago lowered the maximum permissible limit of As from 50 to 10 µg L-1, including rural and small communities (< 2 000 people). Assuming historic accumulation of low level As levels on the internal surfaces of pipe scales and/or SBC, despite meeting the 10 µg As L-1 regulatory limits in As-impacted areas, may have resulted in a distinct As concentration gradient at the pipe surface-flowing water interface and the water. If no changes in the UDWDS water quality are foreseen, historically dormant As will remain tenaciously sorbed by pipe scales. However, the tendency to increase chlorination levels during summer in Mediterranean countries could create the circumstances of producing high concentrations of disinfection by-products. Concurrently, chemisorbed As by pipes may react with formed TTHM / HAA disrupting the pseudo-equilibrium As state, and thus, initiating As release phenomena. This scenario may be most probable in certain areas within the same UDWDS characterised by higher risk formation potential for disinfection by-products, suggesting that such vulnerable areas needs most of the attention from respective water boards. This will contribute to continue safeguarding the quality of potable water in the EU cities against unintentional ingestion exposures to episodic incidences of contaminant release events into tap water.
Contact: Dr Konstantinos C. Makris, Assistant Professor of Environmental Health, Cyprus International Institute for Environmental and Public Health in association with Harvard School of Public Health, Cyprus University of Technology. Irenes 95, Limassol 3041, Cyprus. Telephone: +35-725-002398. Email: konstantinos.makris@cut.ac.cy
List of websites: http://www.cut.ac.cy/waterandhealth/(si apre in una nuova finestra)