Dr Nokubonga Mbanzi (31) is slowly building her profile as one of the astute researchers within the science community. This much was confirmed recently when she graduated as the “first-ever PhD graduate” in the faculty of natural sciences at the Walter Sisulu University (WSU) in the Mthatha campus.
Knowing the marine environment
Dr Mbanzi’s PhD dissertation looked at the impact of pollution along the southeast coast of South Africa, caused mainly by heavy metals that were consumed by shellfish. What made the choice of her area of study more relevant and intriguing was the fact that communities along the coast depend on the shellfish as their primary and supplementary diet. She said it is vital to know the status of the marine environment from which residents sample shellfish as this affects their health status. WHO warns that some of the pollutants like heavy metals found in shellfish may cause health problems like heart disease, kidney failure, and cancer when consumed above the regulatory limit.
Marine limpets and algae
The increasing threat of pollution to the marine environment is of great concern. Marine ecosystems have been observed to store pollutants from other aquatic basins and the surrounding environments for years. The emergence of sickness and disease as a result of the consumption of seafood with contaminants (Potasman 2002; Collado et al. 2006; Lee et al. 2011) has resulted in research on contaminants and their impact worldwide. Consumption of seafood products has considerable health benefits because they contain proteins, vitamins and other nutrients. Seafood products, including fish, are a source of omega-3 polyunsaturated fatty acids (n-3 PUFAs) that can reduce the risk of coronary heart disease, hypertension and diabetes (Sioen et al. 2007). However, contaminants in these seafood products have become a health concern. According to the World Health Organization (WHO), there is evidence that heavy metals can cause damage to the kidney, brain, lungs and nervous system, and also can be carcinogenic (WHO 2007, 2011, 2019).
Heavy metals also have negative effects on aquatic ecosystems when their availability rises above certain levels (Rainbow 2002). They are characterised into two groups: those with biological functions, such as zinc (Zn), copper (Cu), iron (Fe), nickel (Ni) and arsenic (As), and those with no biological importance, such as cadmium (Cd), mercury (Hg) and lead (Pb). Metals that have entered aquatic bodies become trapped in sediments and accumulate in organisms (Phillips 1977). Since heavy metals are nondegradable (Jan et al. 2015), and some are not used by organisms, their accumulation may reach toxic levels (Olmedo et al. 2013). Generally, all organisms take up heavy metals whether they are essential or non-essential, and the fate of the metals depends on the physiology of the organism— n whether the metal is used for metabolic purposes, is stored in the organism’s tissues/organs or binds to other biomolecules (Rainbow 2002). Toxicity of metals essential for metabolic processes, such as Zn, may take some time
According to Dr Mbanzi “heavy metal pollution is an increasing threat to the marine environment and is a major health concern”. She says both marine limpets and algae have been used as biomonitors in some parts of the world, however, there is very little or no data regarding this along the South African coast.
“We investigated heavy metal concentrations in the tissues of selected limpet and algae species sampled at four sites on the southeast coast of South Africa (Silaka, Hluleka, Mthatha and Mbhashe), and determined whether there was any relationship between heavy metal concentrations in the limpets and their algae food sources as evidenced by the trophic transfer factor (TTF),” explains Dr Mbanzi.
Heavy metal concentrations
She says samples were collected in July 2019 and the tissues were digested following normal protocols. Heavy metals were detected using inductively coupled plasma optical emission spectrometry (ICP-OES). “Significant differences in metal concentrations were observed among the algae species. The soft tissues of limpets from Silaka had the highest heavy metal concentrations, and samples from Mthatha had the lowest, with only mercury (Hg) occurring in high concentrations,” she adds.
Bioindicators
Dr Mbanzi says the study observed that metal concentrations in soft tissues were generally 10-times higher than in shell tissues and differed between lower- and upper-shore species. Cadmium (Cd) biomagnified (TTF-1) in all limpet species at all sites. Cd, arsenic (As), lead (Pb) and Hg measured in our study were above the maximum limits set by the South African department of health. “This study suggests that the use of limpet and algae species as bioindicators is feasible since they are widely distributed and can accumulate a wide range of heavy metals,” she adds.
Ilustrious academic career
Born in Cwebeni near Port St Johns, Dr Mbanzi attended Ngubebelu Senior Secondary School. In 2010 she enrolled for a Bachelor’s degree in Microbiology & Zoology. She topped these up with These an Honours Degree in Zoology at the University of Fort Hare. During her MSc degree studies between 2015 and 2016 she was based at the South African Institute for Aquatic biodiversity in Makhanda. In 2017 she did an internship at the South African Observatory Network (Elwandle Node) in Gqeberha.
