SPECIATION OF INORGANIC ANTIMONY IN POLYETHYLENE TEREPHTHALATE (PET) BOTTLED WATER USING HYDRIDE GENERATION ATOMIC ABSORPTION SPECTROPHOTOMETRY

ABSTRACT

Antimony (Sb) is a regulated drinking water contaminant that has been found to leach from polyethylene terephthalate (PET) plastic containers into the waters stored in them. The common inorganic species of antimony in water are Sb(III) and Sb(V), with the former being more toxic and the latter being more soluble. In order to assess the extent to which waters stored in PET bottles are contaminated with inorganic Sb and to further examine the effect of typical storage conditions on migration rates, speciation analysis of inorganic Sb using hydride generation atomic absorption spectrophotometry (HG-AAS) was undertaken on selected PET plastic bottled waters marketed in the Greater Accra Region of Ghana.

Six brands of PET plastic bottled waters were obtained at source on the day of packaging, and analyses undertaken on samples of the waters stored in the plastic containers at intervals of four weeks for twelve weeks, under three carefully chosen storage conditions distinctive of bottled water usage. Selected physicochemical properties of samples of the waters stored in the plastic containers and total Sb of samples of the plastic containers were also determined to discover the effect of some physical properties and certain major ions, and the influence of the different quality PET plastic types on Sb migration respectively.

The study revealed amounts of total Sb in the PET plastic containers of the 6 brands ranging from 123.46 mg/kg to 146.45 mg/kg. The selected physicochemical properties of the waters stored in the PET plastic containers considered were pH (6.78 – 7.43), Ca2+ (1.61 – 12.39 mg/L), Mg2+ (1.00 – 4.96 mg/L), HCO3− (6.18 – 55.41 mg/L) and TDS (8.70 – 70.40 mg/L)). PET bottled waters of 5 out of the 6 brands contained Sb (initial total Sb ranging from 1.11 – 14.65 μg/L) before storage. Total Sb concentrations of the waters stored in the plastic containers were observed to increase with storage time under all the three storage conditions for all the brands of PET plastic bottled waters. Sb(III) and Sb(V) of the waters stored in the

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plastic containers were observed to increase with storage time, with the latter in higher amounts in solution under all the three storage conditions. Waters stored in plastic containers exposed to harsh conditions of the weather like high air temperatures (average temperature for 12 weeks: 23.0ºC in the morning and 39.5ºC in the afternoon) and sunlight outdoors registered the highest Sb concentrations.

In conclusion, PET bottled waters marketed in the Greater Accra region were not found to be contaminated with Sb leaching from their packaging PET plastic containers within the one year limited time of expiry using WHO MCL. Notwithstanding that, harsh weather conditions outdoors is most likely to contribute to the rapid migration of the metalloid (Sb) from the plastic containers, making the bottled water unwholesome before its due expiry time is reached.