Sequential Extractions and Toxicity Potential of Trace Metals Absorbed into Airborne Particles in an Urban Atmosphere of Southwestern Nigeria

Abstract

The paper investigates the hypothesis that biotoxicities of trace metals depend not only on the concentration as expressed by the total amount, but also on their geochemical fractions and bioavailability. Airborne particles were collected using SKC Air Check XR 5000 high volume Sampler at a human breathing height of 1.5–2.0 meters, during the dry season months from November 2014 to March 2015 at different locations in Akure (7°10′N and 5°15′E). The geochemical-based sequential extractions were performed on the particles using a series of increasingly stringent solutions selected to extract metals (Cd, Cu, Cr, Ni, Pb, Zn, and Mn) into four operational geochemical phases—exchangeable, reducible, organic, and residual—and then quantified using an Atomic Absorption Spectrophotometer. The results showed metals concentration of order Pb > Cr > Cd > Zn > Ni > Cu > Mn. However, most metals in the samples exist in nonmobile fractions: exchangeable (6.43–16.2%), reducible (32.58–47.39%), organic (4.73–9.88%), and residual (18.28–27.53%). The pollution indices show ingestion as the leading route of metal exposure, with noncarcinogenic (HQ) and cancer risk (HI) for humans in the area being higher than 1.0 × 10−4, indicating a health threat.

Chemical Fractionation in Environmental Studies of Potentially Toxic Particulate-Bound Elements in Urban Air: A Critical Review

“…The lack of a uniform terminology also relates to the research subject. In the set of publications reviewed, the research subject was defined as “heavy metal(s)” [ 13 , 16 , 17 , 23 , 43 , 71 ], “trace metal(s)” [ 24 , 25 , 34 , 41 , 44 , 75 ] and “trace element(s)” [ 10 , 11 , 14 , 26 , 27 , 45 ]. All three terms appeared in similar numbers.…”

“…Field blank filters were collected to reduce gravimetric bias due to filter handling during and after sampling [ 30 , 80 ]. APM samples were collected at the height of 1–6 m [ 14 , 21 , 25 , 28 , 43 , 45 , 61 , 64 , 69 , 77 ], 12–20 m (roofs of buildings) [ 9 , 16 , 23 , 34 , 44 , 47 , 64 , 80 ] and in a few cases even at 30–35 m [ 76 , 81 ]. Low-volume and high-volume samplers were used exclusively, which, for the most frequently collected 24 h aerosol samples, was associated with the flow of several dozen or several thousand cubic meters of air.…”

“…The Tessier procedure was employed relatively infrequently [ 9 , 25 , 45 , 52 ]. The introduced modifications consisted in determination of the water-soluble fraction of PTEs prior to the conventional procedure [ 45 , 52 ] and in the combined release of the carbonates fraction and the Fe/Mn oxides fraction by leaching with NH 2 OH∙HCl/25% AcOH solution at 96 °C for 6 h [ 25 ]. The Obios procedure was used only according to the original version [ 53 , 77 , 85 ].…”

“…Formally, this review covers the papers published in the last three decades. In fact, 60% of them were published in the last decade [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ] and 30% were published in the years 2001–2010 [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ]. The studies on operational speciation of PTEs dealt primarily with air quality in Europe (40%) [ 6 , 10 , 11 , 14 ,…”

“…The studies on operational speciation of PTEs dealt primarily with air quality in Europe (40%) [ 6 , 10 , 11 , 14 , 19 , 20 , 28 ] and Asia (40%) [ 7 , 8 , 9 , 12 , 13 , 15 , 16 , 17 , 21 , 22 , 23 , 29 , 30 , 31 , 32 , 33 ]. The other studies were conducted in the Americas [ 27 , 35 , 43 , 48 , 52 , 56 , 57 ] and Africa [ 18 , 24 , 25 ]. Thus, this review concerns urban areas of different population sizes with low or high industrial activity, with various agricultural influences and with dry and wet climates.…”