Red Dust! Dead Dust?
The iron ore port in Saldanha Bay showing the red dust deposits. Photo: Ashraf Hendricks for GroundUp.
The Saldanha Bay Municipality, located on the west coast of South Africa in the Western Cape, hosts the Saldanha Bay port. This is the largest iron ore export port in Africa, handling around 67 million tonnes of cargo annually, functional since 1976. Industries in the vicinity of the port rely heavily on ore transported from the Northern Cape by trucks and rail.
Saldanha Bay is home to more than 130 000 inhabitants (https://sbm.gov.za/statistics/), including those who live in informal settlements. In addition, the adjacent Langebaan Lagoon is an important nesting and feeding site for large flocks of migratory birds during the summer months. It forms part of the West Coast National Park, a region renowned for its spectacular spring wildflower displays.
A significant increase in cargo handling during the late 1990’s early 2000’s may have led to increasing dust fallout. Prevailing south-westerly winds from the Atlantic Ocean redistribute this ore-derived dust throughout the town and wider area, resulting in the deposition of red particulate matter on roads, buildings, trees, and nearby water bodies.
This red dust not only deteriorates appearance but may also affect air quality and pose a potential risk to human health. The World Health Organization (WHO) reports that air pollution is the world’s worst environmental health risk, indicating that – globally – more than seven million people die prematurely due to air pollution every year.
To address these possible environmental and health hazard concerns, as well as the staining of buildings and vegetation, Saldanha Bay Municipality started monitoring the dust fallout in 2015. In addition, the municipality started a collaboration with the Department of Earth Science at Stellenbosch University and at UCT to address these air quality challenges.
The research team, under Prof. Susanne Fietz's guidance at Stellenbosch University, set-up additional dust fallout monitoring from 2018 alongside the municipality’s efforts and included measuring the dust metal composition and analysing wind patterns at eight different locations around Saldanha Bay to identify hot spots, assess potential sources and evaluate potential threats for human health.
Identifying the sources is important, as pollutants carried with the dust can be generated not only from ore or cargo handling but also from household, industries, vehicles, etc. On the other hand, not all dust adversely affects human health. Some, but not all dust particles are so fine (e.g. thinner than human hair) that they can inhaled,be inhaled, leading to pulmonary diseases.
Our monitoring programme focusses on these fine particles in the Saldanha Bay area using different sensors including custom-built sensors. These long-term observations show that the fine inhalable dust particles, smaller than 2.5-micrometers, scientifically called PM2.5 in the air, were mostly within the recommended annual average concentrations, exceeding only occasionally the South African National Air Quality Standard (NAAQS) guidelines of a daily average threshold of 40 μg m-3. The higher levels of PM2.5 were mostly observed in late winter and early spring.
These research findings were published in the international scientific peer-reviewed Air Quality, Atmosphere & Health journal (https://doi.org/10.1007/s11869-024-01581-8 ). South Africa aims to reduce daily PM2.5 emissions nationwide to less than 20 μg m-3 by 2030, and hence the continuation of such long-term monitoring will remain crucial.
Example of the PM2.5 sensors used at the Saldanha Bay Municipality: A commercial PurpleAir sensor (panel a), and PM2.5 sensing devices developed by Dept. Of Electrical and Electronic Engineering at Stellenbosch University (panels b and c). Photo: Stellenbosch University
In addition to monitoring the total dust loads and fluxes, it is important to evaluate the chemical composition to assess the potential adverse human health and ecosystem impacts. The dust particles are not homogenous; they are made of a complex mixture of soil, ore dust, and other urban emissions.
The team at Stellenbosch University therefore collected dust particles using a diverse array of sampling devices, particularly devices for passive sampling (i.e. gravitational deposition) and active sampling (i.e. pumping air). The collected dust particles are analysed in the laboratories for the chemical composition, with a specific focus on the metal composition. Several metals are known to affect human health upon exposure to concentrations exceeding recommended guidelines. Our long-term passive samplers in and around the residential areas indicate that metal concentrations largely remain within the guidelines, not indicating imminent exposure risks.
Three sampling set-ups: The photo on the left shows two passive sampling devices: one set-up where particles transported with the wind horizontally enter the dust trap and settle in the trap, and a second ‘bucket’-type sampler in which dust particles settle gravitationally. The photo and schematic illustration on the right shows an active sampling device, called a High-Volume Aerosol Sampler, which filters 1000 liters of air per minute and collects suspended particles in the air (i.e. ‘dust’) on clean filter paper. Photo: Stellenbosch University
Nevertheless, our snap-shot active sampling in the Industrial Development Zone, which means close to the emission sources, indicated that the concentration of a few metals in the air, such as manganese and chromium, exceeded the US EPA guidelines for industrial and residential standards on the sampled days. Our research thus helps create awareness and serves to advise municipalities and stakeholders. In addition, we also calculated indicators of potential human health impacts. This so-called hazard index reflects generally low levels of risk in the area, but again a potential for adverse effects in the Industrial Development Zone (close to the emissions sources) particularly for manganese, cobalt and zinc.
We conclude that although the measured metal concentrations do not currently indicate an immediate risk to human health, areas with elevated metal levels warrant continue monitoring. This is particularly important in regions where intensive industrial activities and associated traffic occur near formal and informal residential areas.
Regular, spatially resolved monitoring of metal concentrations is therefore recommended to detect potential changes in exposure and to support informed environmental management. These findings were published in the scientific peer-reviewed Clean Air Journal (https://doi.org/10.17159/caj/2025/35/2.22227) and in our latest open access translational delivery report (https://doi.org/10.5281/zenodo.20614755).
In addition to our current research on continued monitoring of PM2.5 and potential health impact of different metals, we are working on different chemical tracers to decode these complex dust mixtures originating from different sources and identify major contributing sources of dust such as ore transport, industries, vehicles and households.