A global reconnaissance of particulates and metals/metalloids in untreated drinking water sources

Abstract

Metal and metalloid contamination in drinking water sources is a global concern, particularly in developing countries. This study used hollow membrane water filters and metal-capturing polyurethane foams to sample 71 drinking water sources in 22 different countries. Field sampling was performed with sampling kits prepared in the lab at Hope College in Holland, MI, USA. Filters and foams were sent back to the lab after sampling, and subsequent analysis of flushates and rinsates allowed the estimation of suspended solids and metal and other analayte concentrations in source waters. Estimated particulate concentrations were 0-92 mg/L, and consisted of quartz, feldspar, and clay, with some samples containing metal oxides or sulfide phases. As and Cu were the only analytes which occurred above the World Health Organization (WHO) guidelines of 10 μg/L and 2000 μg/L, respectively, with As exceeding the guideline in 45% of the sources and Cu in 3%. Except for one value of ~ 285 μg/L, As concentrations were 45-200 μg/L (river), 65-179 μg/L (well), and 112-178 μg/L (tap). Other metals (Ce, Fe, Mg, Mn, Zn) with no WHO guideline were also detected, with Mn the most common. This study demonstrated that filters and foams can be used for reconnaissance characterization of untreated drinking water. However, estimated metal and other analyte concentrations could only be reported as minimum values due to potential incomplete retrieval of foam-bound analytes. A qualitative reporting methodology was used to report analytes as "present" if the concentration was below the WHO guideline, and "present-recommend retesting" if the concentration was quantifiable and above the WHO guideline.

Keywords: Global water reconnaissance; Metal/metalloid contamination; Point-of-use water filters; Untreated-drinking water.

Fig. 1

Map of countries where untreated drinking water was sampled in this study

Fig. 2

Schematic of bucket and filter sample collection method as used in the field

Fig. 3

Schematic illustrating the laboratory back-flushing procedure to retrieve the suspended load particulates sampled in the field

Fig. 4

Schematic illustrating the field sample collection process utilizing polyurethane foam blocks (black rectangles) for the capture of dissolved analytes

Fig. 5

Standard curves of light attenuation versus TSS for model particulate suspensions. Correlation coefficients (R²) were > .99 for all curves except for calcite, which was .98

Fig. 6

Processing flow chart scheme for estimating the field concentration of dissolved analytes in untreated drinking water sources based on the analysis of foam rinsates. MDL = method detection limit and LOQ = limit of quantification

Fig. 7

TSS results for different types of untreated drinking water sources sampled in this study

Fig. 8

Categorization scheme for various target analyte concentrations determined in samples. MDL = method detection limit and LOQ = limit of quantification. ND/NS = non-determinable/not significant; P = present, but not quantifiable; P_rt = quantifiable; WHO = World Health Organization guideline

Fig. 9

Total quantifiable dissolved analytes estimated in drinking water sources. Totals represent the sum of all dissolved analytes detected at concentrations above the respective LOQs

Fig. 10

Dissolved As concentrations estimated for the drinking water sources sampled

Fig. 11

Dissolved As concentrations versus TSS in water sources with quantifiable As levels