Trace Element Analysis, Model-Based Clustering and Flushing to Prevent Drinking Water Contamination in Public Schools

Carter, Jake A.; Jones, Bradley T.; Donati, George L.

doi:10.21577/0103-5053.20180199

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Articles • J. Braz. Chem. Soc. 30 (3) • Mar 2019 • https://doi.org/10.21577/0103-5053.20180199 copy

Trace Element Analysis, Model-Based Clustering and Flushing to Prevent Drinking Water Contamination in Public Schools

Authorship SCIMAGO INSTITUTIONS RANKINGS

Drinking water samples taken from cafeteria sinks and water fountains in each of the 76 schools in the Winston-Salem/Forsyth County Schools (WSFCS) district (North Carolina, United States) were analyzed by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) to determine As, Cd, Cr, Cu, Pb, Sb, Se and Tl. All samples from currently active schools tested below the maximum contaminant level (MCL) set for each element. Model-based clustering was employed to identify schools more prone to drinking water contamination. This multivariate approach may be used in a prevention program that can be tailored to specific school districts, with each school tested at a frequency compatible with its contamination risk level. Water flow stagnation during the summer break results in higher elemental concentrations in school drinking water, but a simple 5-60 min flushing procedure significantly reduces the contamination levels.

Keywords:
drinking water contamination; ICP-MS; multivariate analysis; water flow stagnation; preventive flushing

Instrument parameter	Operating condition
Radio frequency applied power / kW	1.550
Sampling depth / mm	10.0
Nebulizer	concentric nebulizer, glass
Spray chamber	Scott type, double pass
Makeup gas flow rate / (L min^-1)	0.0
Carrier gas flow rate / (L min^-1)	1.05
Octopole bias / V	-18.0
KED / V	5.0
Operating mode	MS/MS (on mass)
Collision/reaction cell gas	H₂
Collision/reaction cell gas flow rate / (mL min^-1)	4.0
Monitored m/z	75 (As), 111 (Cd), 52 (Cr), 63 (Cu), 208 (Pb), 121 (Sb), 78 (Se) and 205 (Tl)

Element	LOD / (µg L^-1)	LOQ / (µg L^-1)	Recovery^a a The numbers in parentheses are the certified concentrations for each element in µg L-1. LOD: limit of detection; LOQ: limit of quantification. / %
As	0.04	0.1	94 (60.45)
Cd	0.02	0.1	98 (6.568)
Cr	0.08	0.3	95 (20.40)
Cu	0.3	0.9	91 (22.76)
Pb	0.01	0.04	93 (19.63)
Sb	0.01	0.02	92 (58.30)
Se	0.06	0.2	95 (11.97)
Tl	0.004	0.01	87 (7.445)

Concentration / (µg L^-1)	Cafeteria sink (n = 73)			Water fountain (n = 75)			MCL or AL
Concentration / (µg L^-1)	Mean	Min	Max	Mean	Min	Max	MCL or AL
As	0.070	< LOD	0.19	0.060	< LOD	0.16	10
Cd	N.D.^a a Not determined (N.D.), as more than 50% of observations were below the respective LODs. MCL: maximum contaminant level; AL: action level; LOD: limit of detection.	< LOD	0.39	N.D.^a a Not determined (N.D.), as more than 50% of observations were below the respective LODs. MCL: maximum contaminant level; AL: action level; LOD: limit of detection.	< LOD	0.29	5
Cr	0.15	< LOD	0.49	0.16	< LOD	0.47	100
Cu	19	2.0	69	34	9.6	110	1300
Pb	0.32	< LOD	5.0	0.26	< LOD	4.9	15
Sb	0.070	0.030	0.58	0.060	0.030	0.43	6
Se	N.D.^a a Not determined (N.D.), as more than 50% of observations were below the respective LODs. MCL: maximum contaminant level; AL: action level; LOD: limit of detection.	< LOD	0.14	N.D.^a a Not determined (N.D.), as more than 50% of observations were below the respective LODs. MCL: maximum contaminant level; AL: action level; LOD: limit of detection.	< LOD	0.25	50
Tl	N.D.^a a Not determined (N.D.), as more than 50% of observations were below the respective LODs. MCL: maximum contaminant level; AL: action level; LOD: limit of detection.	< LOD	0.010	N.D.^a a Not determined (N.D.), as more than 50% of observations were below the respective LODs. MCL: maximum contaminant level; AL: action level; LOD: limit of detection.	< LOD	0.010	2
Building year	1969	1923	2012	1971	1923	2012	-

School location	Cafeteria			Fountain			Building year
School location	Cu / (µg L^-1)	Pb / (µg L^-1)	Group	Cu / (µg L^-1)	Pb / (µg L^-1)	Group	Building year
School year
A	16	0.83	2	31	0.41	3	1978
B	47	0.18	1	69	0.080	4	1991
C	70	2.3	2	110	0.62	2	1956
D	9.1	0.11	4	15	0.070	3	1959
After summer break
A	6.8	0.37	2	270	0.83	3	1978
B	49	0.080	1	110	1.1	4	1991
C	39	4.2	2	100	1.8	2	1956
D	59	0.15	4	52	0.030	3	1959

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