1 Drinking Water Quality – Safety and Public Health Risk Dr. Steve E. Hrudey, FRSC, FSRA, PEng Professor Emeritus University of Alberta.

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Drinking Water Quality – Safety and Public Health Risk

Dr. Steve E. Hrudey, FRSC, FSRA, PEng

Professor EmeritusUniversity of Alberta

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A National Collaboration on Risk

♦ The Municipal Water Management Research Consortium was created by the: Canadian Water Network, Alberta Water Research Institute Ontario Centres of Excellence

♦ Municipal water leaders posed the question: “How best can drinking water providers address risk and uncertainty to assure safe drinking water?”

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A National Collaboration on Risk♦ International Expert Panel:

John Fawell, U.K. William Leiss, Canada Joan Rose, U.S.A. Martha Sinclair, Australia Chair, Steve Hrudey, Canada

♦ User Advisory Panel Ted Gillespie, Camrose Ian Douglas, Ottawa John Cooper, Canada Donald Reid, Alberta

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What Are the Problems with Risk?♦ An unmanageable number of potential drinking water

contaminants with the list growing♦ Detection limits are improving so contaminants will be

detected in future where they were not detected in the past

♦ Public expectations for “safe” water are not well defined, but are certain to be undermined by exotic chemical detection without context

♦ Lack of understanding by media, and even some relevant professionals about the relative significance of newly detected contaminants

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An Illustration of the Problem

♦ e.g. Suzuki Foundation (2006) “the water we drink”

Recommendation #1: “the GCDWQ should be replaced with …binding national standards… that are equal to or better than the highest standards provided in any other industrialized nation.”

6Recommendations for new Canadian MAC guidelines

POLLUTANT RECOMMENDED CANADIAN

STANDARD (mg/L) CURRENT CANADIAN

GUIDELINES (mg/L) 2,4-D 0.0001 (E.U., AUS.) 0.1

Aldicarb 0.0001 (E.U.) 0.009

Aldrin and dieldrin 0.00001 (AUS.) 0.0007

Antimony 0.003 (AUS.) 0.006

Arsenic 0.007 (AUS.) 0.01

Atrazine 0.0001 (E.U., AUS.) 0.005

Azinphos-methyl 0.0001 (E.U.) 0.02

Barium 0.7 (AUS., WHO) 1.0

Bendiocarb 0.0001 (E.U.) 0.04

Benzene 0.001 (E.U., AUS.) 0.005

Boron 0.5 (WHO) 5.0

Bromoxynil 0.0001 (E.U.) 0.005

Cadmium 0.002 (AUS.) 0.005

Carbaryl 0.0001 (E.U.) 0.09

Carbofuran 0.0001 (E.U.) 0.09

Carbon tetrachloride 0.0001 (E.U.) 0.005

Chlorpyrifos 0.0001 (E.U.) 0.09

Cyanazine 0.0001 (E.U.) 0.01

Cyanide 0.05 (E.U.) 0.2

Cyanobacterial toxins 0.0013 (AUS.) 0.0015

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An Illustration of the Problem♦ Many of the lower numbers were based on

detection limits as a futile surrogate for zero rather than on health risk assessment

e.g. for 2,4-D, Australia, EU was based on a detection limit of 0.0001 mg/L;

at 0.0000999 mg/L 2,4-D would be reported as “non-detectable”

that non-detectable but non-zero value could still correspond to at least 2,721,260,000,000 molecules of 2,4-D per litre of water

as detection limits continue to decrease, drinking water limits could be lowered more than another trillion-fold according to this logic

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An Illustration of the Problem♦ Simply adding contaminants to a monitoring list

only adds cost but does little to assure safety♦ WHO Water Safety Plan and Australian Risk

Management approach correctly focus on performance of water safety barriers

♦ Focus only on monitoring treated water for MACs distracts from focus on barrier performance and is unmanageable for small and medium operators

♦ Even if resources were not an issue, there is an inescapable reality that monitoring for rare hazards encounters diminishing returns Hrudey & Leiss (2003), Hrudey& Rizak (2004), Rizak & Hrudey (2006)

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Industry & Academic Survey (Rizak & Hrudey 2006 Env.Sci.Technol. 40:5244-5250)

♦ Explored the degree of understanding of the quantitative interpretation of monitoring evidence with 2 professional surveys

♦ Australian Water Association members - Operators, Public health, Water supply, Water management, law and policy

• 352 respondents• 63% > 10 years experience (38.1% >20 years)• 42% directly involved with interpreting/decision-

making♦ Association of Environmental Engineering &

Science Professors, i.e. the teachers

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Monitoring evidence for a city has indicated that in treated drinking water, a pesticide, say atrazine, is truly present above the recognised standard methods detection limit once in a 1000 water samples from consumers’ taps.The analytical test for the pesticide has the following characteristics:95% of tests will be positive for detection when the contaminant is truly present, 98% of tests will be negative for detection when the contaminant is truly not present above the detection limit.

Hypothetical Monitoring Scenario to Evaluate Use of Evidence

With these characteristics, given a positive result (detection) on the analytical test for the pesticide in the drinking water system, how likely do you think this positive result is true? Provide your scale of agreement below: almost certain (95 to 100%) highly unlikely (5 to 20%) highly likely (80 to 95%) extremely unlikely (0 to 5%) more likely than not (50 to 80 %) Don’t know less likely than not (20 to 50%)

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Results CORRECT ANSWER FOR THE INFORMATION SUPPLIED IS

4.54% or Extremely unlikely (0 to 5%)

2.0

9.77.1

36.1

8.2

4.3

32.4

25.5

29.6

5.13.1

5.1

23.5

5.1

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

Almost certain (95 - 100%)

Very likely (80 - 95%)

More likely thannot (50 - 80%)

Less likely thannot (20 - 50%)

Very unlikely (5 - 20%)

Extremelyunlikely (0 - 5%)

Don't know

Confidence estimate

Pro

po

rtio

n o

f su

rvey

gro

up

Water professionals

Environmental engineering / scienceprofessors

An American academic commented that “past evidence or ‘best intelligence’ play no direct role as the law specifies that actual monitoring data at each sampling point should be used”

All that mattered to him was whether you are above or below the regulatory limit according to “analytical results.”

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Meaning for Risk Management♦ For detecting hazards we need to know

the Positive Predictive Value, PPV PPV is:

• given that you get a positive, how likely is it truly present?

NOT the Diagnostic Sensitivity • given the true presence, how likely will it test positive?

to understand what is our ability to avoid false positive errors

♦ PPV is strongly a function of the frequency of the danger that we are looking for

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α = false positive rate β = false negative rate

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Implications: Water Quality Monitoring

♦ Medical diagnostic screening programs e.g. breast cancer screening (Meyer et al. 1990. JAMA 263: 2341-2343) for women < 50 yr; PPV 8.8% (~11 false

positives per true positive) for women > 50 yr; PPV 32% (~2 false positives

per true positive) ♦ Hypothetical water quality example for Giardia

cysts assuming: Diagnostic Sensitivity = 80%, Diag. Specificity = 90%Raw polluted water (est. cyst prev. ~63%) PPV = 93%Raw water protected (est. cyst prev. ~16%) PPV = 60%Treated water (est. cyst prev. ~1%) PPV = 7.5%

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Rizak, S. & S.E. Hrudey. 2007. Strategic Water Quality Monitoring for Drinking Water Safety. Research Report No 37. CRC for Water Quality and Treatment. Australia.

www.waterquality.crc.org.au/publications/report37_strategic_water_monitoring.pdf

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Improving Information Value

♦ Make full use of context (supporting evidence)♦ Use sequential confirmatory testing

Airport screening (check the positives) Drug testing at Olympics (analyze a split sample)

♦ Use parallel testing♦ Use targeted or strategic testing

Higher contamination locations Event monitoring with higher hazard frequency

♦ Ultimately, the monitoring must be used in a meaningful context, NOT as a misleading compliance exercise

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What is Safe Drinking Water?

♦ No current legislation in Canada, including the Ontario Safe Drinking Water Act or the U.S. Safe Drinking Water Act define safe drinking water.

♦ The World Health Organization (2004) Drinking Water Guidelines state: “Safe drinking-water, as defined by the Guidelines, does not represent any significant risk to health over a lifetime of consumption, including different sensitivities that may occur between life stages.”

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What is Safe Drinking Water?

♦ Walkerton Inquiry Report - A Strategy for Safe Drinking Water (O’Connor 2002, p.75): “The goal of any drinking water system should be to deliver water with a level of risk that is so negligible that a reasonable and informed person would feel safe drinking it.”

♦ Bonn Charter (IWA 2004) commits to provide: “Good safe drinking water that has the trust of consumers.”

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What is Risk?To understand negligible risk, must understand riskRisk is a multidimensional prediction of what can go

wrong consisting of the following elements:♦ Hazard – the potential to cause harm♦ Probability – the likelihood that specified harm

will occur for a specified scenario♦ Consequences – the nature of harm that occurs♦ Time-frame – the duration over which the risk is

quantified♦ Personal perspectives of those affected about

what is important to them

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What is Safe Drinking Water?

♦ Safe drinking water means something like:water of such consistent quality, posing no significant health risk, that a reasonable, accurately informed consumer need have no health concerns sufficient to justify seeking alternatives

♦ A formal working definition is still under discussion, but safe inevitably includes some aspect of consumer judgement & confidence

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What is Being Developed?

♦ A risk hierarchy based on evidence for drinking water including uncertainty

♦ Illustrations of how to use the hierarchy♦ Explanation of how risk assessment has been

used to develop DW guideline MAC numbers♦ A tool kit for informing consumers♦ Examples of using a Water Safety Plan

approach to assuring safe drinking water♦ Rationale for strategic water quality monitoring♦ Quality assurance advice for water quality data

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