Overview
Klopper and colleagues measured inorganic elements and water-soluble ions in PM10 aerosols at the Henties Bay Aerosol Observatory on the Namibian coast and used positive matrix factorisation to apportion sources. This is upstream atmospheric-deposition and source-attribution evidence: it does not measure bottled water or a finished product, but it identifies heavy-metal aerosol burdens and likely source classes that can deposit to coastal land and marine systems.
Key numbers
The study collected 385 PM10 filter samples over 26 non-consecutive weeks in 2016 and 2017. Table 1 reports mean elemental concentrations in ng m−3 with ranges across the full dataset: aluminum (Al) 478 ± 581, range 2-4739; Fe 367 ± 458, range 3-3687; Mn 13 ± 11, range 1-86; Zn 12 ± 7, range 1-42; chromium (Cr) 8 ± 6, range 1-31; V 8 ± 5, range 1-38; Ba 9 ± 7, range 1-34; Co 8 ± 5, range 1-32; Cu 13 ± 9, range 1-48; nickel (Ni) 8 ± 6, range 1-33; cadmium (Cd) 735 ± 1124, range 1-6776; arsenic (As) 191 ± 317, range 1-1092; and lead (Pb) 75 ± 89, range 1-509. Table 1 also reports Sr 77 ± 63 ng m−3 and Nd 15 ± 11 ng m−3, which are source-apportionment tracers in this paper but do not currently have HMI metal pages.
Positive matrix factorisation identified five PM10 components: sea salt 74.7 ± 1.9% of total estimated mass, mineral dust 15.7 ± 1.4%, ammonium-neutralised aerosol 6.1 ± 0.7%, fugitive dust 2.6 ± 0.2%, and industry 0.9 ± 0.7%. The authors state that the PMF fugitive-dust component was traced by V, Cd, Pb, Nd, and Sr, while the industry component was characterised by As, Zn, Cu, Ni, and Sr.
Section 4.2.3 reports annual mean V concentrations of 9 ± 5 ng m−3 in 2016 and 7 ± 6 ng m−3 in 2017, and annual mean Ni concentrations of 8 ± 7 ng m−3 in 2016 and 7 ± 4 ng m−3 in 2017. The authors interpret V as associated preferentially with mineral dust and fugitive dust, with mining activities and heavy-oil combustion as plausible contributors, while Ni is associated preferentially with the industry component and heavy-oil combustion.
For other heavy metals, Section 4.2.3 states that the mean Pb concentration was 75 ± 89 ng m−3 and that the PMF model separated the largest fractions of Zn and Pb into industry and fugitive-dust components, respectively. The mean Cd concentration was 1502 ± 1458 ng m−3 in 2016 and 219 ± 163 ng m−3 in 2017, with the 2016 elevation attributed mainly to high October 2016 concentrations that coincided with high concentrations of most other heavy metals except As. Section 4.2.5 reports annual mean As concentrations of 22 ± 16 ng m−3 in 2016 and 239 ± 344 ng m−3 in 2017.
The abstract attributes V, Cd, Pb, and Nd to fugitive dust emitted from bare surfaces or mining activities. It attributes As, Zn, Cu, Ni, and Sr to combustion of heavy oils in commercial ship traffic across the Cape of Good Hope sea route, power generation, smelting, and other regional industrial activities. The conclusion states that PMF identified mining activities, including road-construction-related mining, as a distinct contributor for most heavy metals and that atmospheric deposition of trace metals including Cr, Cu, Ni, Mn, and Zn could affect marine productivity in the Benguela Upwelling System.
Methods (brief)
PM10 samples were collected at HBAO, approximately 100 m from the shoreline, using a Thermo Fisher Scientific Partisol 2025i sampler with a certified PM10 inlet and 47 mm Whatman Nuclepore polycarbonate filters. Sampling used 9 h daytime and nighttime filters, yielding 385 samples. Elemental concentrations for 24 elements including Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Sr, Pb, Nd, Cd, and Ba were measured by wavelength-dispersive X-ray fluorescence. Water-soluble ions were measured by ion chromatography. Source apportionment used temporal correlations, HYSPLIT back trajectories, local wind data, and EPA PMF 5.0.
Related evidence
- Atmospheric deposition of heavy metals
- Source attribution and environmental burden apportionment
- Aquatic bioaccumulation of heavy metals
- Cadmium
- Lead
- Arsenic, Total
- Nickel
- Chromium
- Copper
- Manganese
- Zinc
- Iron
- Cobalt
- Barium
- Aluminum
- Vanadium
Update history
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