Monitoring of trace metal accumulation in two South African farmed mussel species, Mytilus galloprovincialis and Choromytilus meridionalis

The Status of Marine Mussel Pollution Research in South Africa (2012-2022)

The growing human population requires more food each year, and seafood products can help meet this demand if clean water resources are available for their growth. Farmed and wild mussels are environmentally friendly seafood with many health benefits to human consumers, but they can also pose a health risk if they are harvested from areas where marine anthropogenic pollution is uncontrolled or unmonitored. While the coastline in South Africa has long been assumed to be pristine, a growing number of recent studies are raising contamination concerns. Baseline studies establish a wide range of anthropogenic pollutants to be present in the marine environment, specifically in urbanised or industrialised areas like major cities or harbours. This review summarises how mussels could pose health risks to human consumers and the current research that is being conducted by private researchers and institutions in South Africa. The review emphasises the need for more research in the field and for governmental pollution monitoring data to be released to the public.

Seasonal variations in mercury, cadmium, lead and arsenic species in Norwegian blue mussels (Mytilus edulis L.) - Assessing the influence of biological and environmental factors

BACKGROUND

Blue mussels (Mytilus edulis L.) can accumulate undesirable substances, including the potentially toxic elements (PTEs) cadmium (Cd), mercury, (Hg), lead (Pb), arsenic (As) and As species. In this study, the levels of PTEs and As species were determined in samples of blue mussels to assess the influence of environmental and biological factors, and evaluate the potential risk associated with blue mussels in terms of food and feed safety.

METHODOLOGY

Blue mussels were collected monthly from one location in Western Norway from February 2018 to December 2018, and from April 2019 to April 2020. Samples were analyzed for PTEs using inductively coupled plasma mass spectrometry (ICP-MS), and high-performance liquid chromatography (HPLC) coupled to ICP-MS. Temperature, salinity and fluorescence (chlorophyll a) were monitored in the seawater column by STD/CTD, to assess the potential influence of these environmental factors on the PTE levels in the mussels.

RESULTS

The results showed seasonal variations in the PTEs, with somewhat higher concentrations in spring and winter months. Unusually high levels of total As (101.2 mg kg^-1 dw) and inorganic As (53.6 mg kg^-1 dw) were observed for some of the time points. The organic As species arsenobetaine was generally the major As species (17-82% of total As) in the mussels, but also simple methylated As species and arsenosugars were detected. Principal components analysis (PCA) did not show a consistent relationship between the environmental factors and the PTE concentrations, showing contrary results for some elements for the periods studied. The condition index (CI) could explain variations in element concentration with significant correlations for Cd (r = -0.67, p = 0.009) and Pb (r = -0.62, p = 0.02 in 2019/20 and r = -0.52, p = 0.02 in 2018), whereas the correlation between As and CI was not significant (r = 0.12 in 2018, and r = -0.06 in 2019/20). Higher concentrations of iAs and arsenosugars coincided with increased signals of chlorophyll a, suggesting that phytoplankton blooms could be a source of As in the blue mussels.

CONCLUSION

To our knowledge, this is the first study of As species in blue mussels collected over a time period of two years, providing an insight into the natural variations of these chemical forms in mussels. In terms of mussel as food and future feed material, concentrations of Cd, Hg and Pb were below the maximum levels (MLs) established in the EU food and feed legislation. However, levels of As and iAs in mussels at some time points exceeded the MLs for As in the feed legislation, and the margin of exposure (MOE) was low if these mussels were for human consumption, highlighting the importance of determining the chemical forms of As in feed and food.

Metals and co-presence of other pollutants in mussels (Perna perna) around Algoa Bay: Human consumption safety concerns

Elevated metal concentrations can become harmful to marine organisms and to humans that consume them. Metal concentrations at multiple sites around Algoa Bay, South Africa, were last investigated in the 1980s. We collected wild brown mussels (Perna perna) from seven sites around Algoa Bay, and quantified metallic elements using ICPMS. Metallic element concentrations differed significantly among the sampling sites and correlated with pollution sources at specific sites. The concentration of Pb in mussels at one site slightly exceeded South African limits. Based on the South African estimated daily intake, the target hazard quotient, and South African metal limits, mussels from Algoa Bay are safe for human consumption, except possibly from one site. However, combined with data on bisphenols and benzophenone UV filters in P. perna from the same sites, we suggest a possible health concern to consumers.

Biomonitoring of heavy metals accumulation in molluscs and echinoderms collected from southern coastal India

Distribution of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in molluscan and echinoderm species collected from Kerala and Gulf of Mannar in Southern India is presented. Atomic absorption spectrometry was used to determine metal concentrations. Concentrations of metals showed a descending order of Zn > Cu > Pb > Cd > Cr. Zn and Cu might have originated from both natural and man-made sources. However, Cd, Cr, and Pb could have strong anthropogenic influences such as harbour activities and untreated industrial and agricultural runoff. Bioaccumulation factor (BAF) value of Cd in two edible bivalves from Munambam is slightly greater than one. Regular consumption of Cd-loaded shellfish can cause serious health hazards and concerns to humans. BAF results showed that Zn, Cu, Pb, and Cd were more bioaccumulated and beyond the threshold limits in certain species. It is evident that consumption of shellfish from the Kerala coastal waters may have adverse health impacts to the consumers.

Seasonal variations and human health risk assessment of trace elements in the bivalve ecosystem in the Sea of Marmara

Twelve trace elements were studied in four economically important bivalve molluscs (Mediterranean mussel, manila clam, striped venus clam, and truncated wedge clam) from the southern Marmara Sea for seasonal bioaccumulation and human health risk assessment. According to the findings, Fe and Zn were the most accumulative and element concentrations changed considerably (P < 0.05) between seasons and species. Daily, weekly, monthly intake and target hazard quotients of the trace elements were estimated and compared with maximum limits. The results revealed that consuming these bivalve molluscs from the southern Marmara Sea could be considered safe for human consumption. Nevertheless, further monitoring is needed in order to better follow the development in time of elemental pollution due to increasing environmental pressure on the Marmara Sea basin, together with research on other different bioaccumulative organisms.

Arsenic Exposure via Contaminated Water and Food Sources

Arsenic poisoning constitutes a major threat to humans, causing various health problems. Almost everywhere across the world certain “hotspots” have been detected, putting in danger the local populations, due to the potential consumption of water or food contaminated with elevated concentrations of arsenic. According to the relevant studies, Asia shows the highest percentage of significantly contaminated sites, followed by North America, Europe, Africa, South America and Oceania. The presence of arsenic in ecosystems can originate from several natural or anthropogenic activities. Arsenic can be then gradually accumulated in different food sources, such as vegetables, rice and other crops, but also in seafood, etc., and in water sources (mainly in groundwater, but also to a lesser extent in surface water), potentially used as drinking-water supplies, provoking their contamination and therefore potential health problems to the consumers. This review reports the major areas worldwide that present elevated arsenic concentrations in food and water sources. Furthermore, it also discusses the sources of arsenic contamination at these sites, as well as selected treatment technologies, aiming to remove this pollutant mainly from the contaminated waters and thus the reduction and prevention of population towards arsenic exposure.

Occurrence of heavy metals and their removal in Perna viridis mussels using chemical methods: a review

Despite the nutritional benefits, bivalves like mussels are also an excellent aquatic heavy metal biomonitoring agent due to their high tolerance to varying levels of temperature, salinity and oxygen, as well as pollutants. Although the accumulated toxic heavy metals may not exert direct negative impacts on the mussels, such toxicants in mussel tissues can give harmful effects on human body when consumed in toxic quantities and/or over prolonged period. The booming of urban and industrial activities, and consequently the increment of runoffs, as well as wastewater effluents and leaching, further exacerbated the magnitude of this issue. Hence, continuous monitoring of heavy metal contents in mussels is vital to ensure its compliance with food safety regulations, protecting consumers at large. This review paper discusses the occurrence of heavy metals in mussels especially that of Perna viridis in Malaysia and other parts of the world since year 2000 until 2021. Heavy metal concentration data and patterns from various coastal and/or estuaries were compared. Where applicable, statistical data that indicate variations between sampling sites, sampling months or years and chemical treatments for heavy metal removal were critically reviewed. Health risk assessment findings were also discussed. More importantly, related chemical-based interventions to minimize and/or eliminate toxic heavy metals from mussels are also reviewed.

Partitioning of trace elements in the tissues of Mediterranean mussels (Mytilus galloprovincialis) sampled from industrial sites along the Algerian coast

This research was aimed at evaluating the seasonal partitioning of Zn, Se, As, Cu, and Co in the tissues of Mytilus galloprovincialis sampled at two industrial sites along the Algerian coast. Adult mussels were seasonally collected from two sites over the course of a whole year. The gills, digestive glands, gonads, and remaining soft tissues were analyzed through ICP-MS. The observations led to identifying metals ranges (μg g^-1_{Dry Weight}) of 67.17-395.51 (Zn), 2.18-12.74 (Se), 7.81-28.61 (As), 3.32-155.91 (Cu), and 0.10-3.59 (Co) in the various tissues. The highest concentrations were found in the digestive glands and gills as compared to the gonads and remaining soft tissues. Distinct patterns of metals partitioning were found: indeed, As and Co concentrations were higher in the digestive glands, while Se and Zn concentrations were higher in the gills. Many of the mussels samples resulted contaminated, therefore potentially posing a considerable health risk to consumers.

Effect of the Elemental Content of Shells of the Bivalve Mollusks (Mytilus galloprovincialis) from Saldanha Bay (South Africa) on Their Crystallographic Texture

Simple Summary

The aim was to study the question of whether the texture of mollusk shells changes with alteration in their elemental composition. Even though significant differences between concentrations of elements among the stations were found, the crystallographic textures of mussel shells from the studied bays showed insignificant dissimilarities. The observed differences in the maximum values in the pole figures fell within the range of variability identified for the genus Mytilus. Nevertheless, they appeared to correlate with the concentrations of Br, Mg, and Sr, which merits further investigation using larger sample sizes and higher variabilities of the ecological state of mussels.

Abstract

A both wild and farmed mussels in natural conditions, anthropogenic inputs are usually reflected in the increase of the content of specific elements. To determine the possible effect of the elemental patterns of farmed and wild mussels (Mytilus galloprovincialis) collected in the Saldanha Bay area (South Africa) on the crystallographic texture of the shells, the content of 20 elements in shells and 24 in the soft tissue of mussels was determined by neutron activation analysis. The crystallographic texture of mussel shells was analyzed using time-of-flight neutron diffraction. The wild mussels from open ocean site live in stressful natural conditions and contain higher amounts of the majority of determined elements in comparison with mussels farmed in closed water areas with anthropogenic loadings. The changes between the maximums of the same pole figures of the three samples are in the range of variability identified for the genus Mytilus. The content of Cl, Sr, and I was the highest in mussels from the open ocean site, which is reflected by the lowest mass/length ratio. The determined crystallographic textures of mussels are relatively stable as shown in the analyzed pole figures despite the concentrations of Na, Mg, Cl, Br, Sr, and I in shells, which significantly differ for wild and farmed mussels. The stability of the crystallographic texture that we observed suggests that it can be used as a reference model, where if a very different texture is determined, increased attention to the ecological situation should be paid.

Herbicides in Camps Bay (Cape Town, South Africa), supplemented

During 2017 the herbicides alachlor, atrazine, butachlor, metolachlor, and simazine were detected in water samples, beach sediments and marine biota collected at Camps Bay, Cape Town, South Africa. During that period, the annual rain catchment record was 77,000 m³, whereas the volume of chemically laden sewage discharged via the marine outfall was 693,500 m³ making the marine sewage outfall by far the most predominant source for these herbicides in the bay. The chemical load in the discharged sewage was not removed by the applied pre-treatment step, which only uses a 3 mm screen to eliminate plastic, paper, rags and other foreign materials. After passing through the Camps Bay pump station, the sewage is released to the bay at the following GPS position 33°56'42.214″ S 18°21'59.257″ E (Colenbrander et al., 2021) and at a discharge depth of 23 m and 1497 m from the beach. In our study the presence in marine biota of atrazine and simazine were taken as being indicative of the chemical signature of the sewage being released through the outfall, since these compounds were detected previously in the sewage prior to discharge. To our knowledge, our studies of the herbicides in diverse benthic organisms found in the near shore environment of Camps Bay are the first of their kind for this Western Cape region.

Seasonal accumulation of trace elements in native Mediterranean mussels (Mytilus galloprovincialis Lamarck, 1819) collected in the Calich Lagoon (Sardinia, Italy)

The occurrence of 21 trace elements in native Mediterranean mussel (Mytilus galloprovincialis) from the Calich Lagoon, a typical brackish area of the northwest of Sardinia (Italy), was investigated. The seasonal variation of metals in bivalves was considered, and the highest values were found in spring and summer; in particular, a high significant (P < 0.001) temporal variation was reported for silver (Ag) and mercury (Hg). The highest and similar concentrations were registered for aluminium (Al, mean 32 mg kg^-1wet weight), iron (Fe, mean 32 mg kg^-1 w. w.), and zinc (Zn, mean 25 mg kg^-1 w. w.). The maximum limits set by European Regulations for cadmium (Cd), mercury (Hg), and lead (Pb) were never exceeded. Speciation analysis revealed negligible risk related to inorganic arsenic (iAs). Therefore, M. galloprovincialis confirmed its role as suitable bioindicator to monitor the contamination of coastal environments. Although the recommended tolerable weekly intake (TWI) was not exceeded, the levels of aluminium should be carefully evaluated in monitoring plans in the studied lagoon. Graphical abstract.

Inorganic Elements in Mytilus galloprovincialis Shells: Geographic Traceability by Multivariate Analysis of ICP-MS Data

The international seafood trade is based on food safety, quality, sustainability, and traceability. Mussels are bio-accumulative sessile organisms that need regular control to guarantee their safe consumption. However, no well-established and validated methods exist to trace mussel origin, even if several attempts have been made over the years. Recently, an inorganic multi-elemental fingerprint coupled to multivariate statistics has increasingly been applied in food quality control. The mussel shell can be an excellent reservoir of foreign inorganic chemical species, allowing recording long-term environmental changes. The present work investigates the multi-elemental composition of mussel shells, including Al, Cu, Cr, Zn, Mn, Cd, Co, U, Ba, Ni, Pb, Mg, Sr, and Ca, determined by inductively-coupled plasma mass-spectrometry in Mytilus galloprovincialis collected along the Central Adriatic Coast (Marche Region, Italy) at 25 different sampling sites (18 farms and 7 natural banks) located in seven areas. The experimental data, coupled with chemometric approaches (principal components analysis and linear discriminant analysis), were used to create a statistical model able to discriminate samples as a function of their production site. The LDA model is suitable for achieving a correct assignment of >90% of individuals sampled to their respective harvesting locations and for being applied to counteract fraud.

A Commentary on the Use of Bivalve Mollusks in Monitoring Metal Pollution Levels

The objective of this commentary is to promote the use of bivalves as biomonitors, which is a part of the continual efforts of the International Mussel Watch. This commentary is an additional discussion on "Bivalve mollusks in metal pollution studies: From bioaccumulation to biomonitoring" by Zuykov et al., published in Chemosphere 93, 201-208. The present discussion can serve as a platform for further insights to provide new thoughts and novel ideas on how to make better use of bivalves in biomonitoring studies. The certainty of better and more extensive applications of mollusks in environmental monitoring in the future is almost confirmed but more studies are urgently needed. With all the reported studies using bivalves as biomonitors of heavy metal pollution, the effectiveness of using Mussel Watch is beyond any reasonable doubts. The challenge is the development of more accurate methodologies for of heavy metal data interpretation, and the precision of the biomonitoring studies using bivalves as biomonitors, whether in coastal or freshwater ecosystems. Lastly, inclusion of human health risk assessment of heavy metals in commercial bivalves would make the research papers of high public interest.

Programmed responses of different life-stages of the seagrass Ruppia sinensis to copper and cadmium exposure

Seagrass meadows are recognized as crucial and are among the most vulnerable habitats worldwide. The aquatic plant genus Ruppia is tolerant of a wide salinity range, and high concentrations of trace metals. However, the tolerance of its early life stages to such trace metal exposure is unclear. Thus, the current study investigated the trace metal-absorbing capacity of three different life-history stages of Ruppia sinensis, a species that is widely distributed in China, by observing toxic symptoms at the individual, subcellular, and transcription levels. The seedling period was the most vulnerable, with visible toxic effects at the individual level in response to 50 μM copper and 500 μM cadmium after 4 days of exposure. The highest concentrations of trace metals occurred in the vacuoles and cytoplasmic structures of aboveground tissues. Genes related to signal identification and protein processing were significantly downregulated after 4 days of exposure to copper and cadmium. These results provide information relating to the strategies evolved by R. sinensis to absorb and isolate trace elements, and highlight the phytoremediation potential of this species.

Manganese in the Diet: Bioaccessibility, Adequate Intake, and Neurotoxicological Effects

Manganese (Mn) is an essential element that participates in several biological processes. Mn serves as a cofactor for several enzymes, such as glutamine synthetase and oxidoreductases, that have an important role in the defense of the organisms against oxidative stress. The diet is the main source of Mn intake for humans, and adequate daily intake levels for this metal change with age. Moreover, in higher amounts, Mn may be toxic, mainly to the brain. Here, we provide an overview of Mn occurrence in food, addressing its bioaccessibility and discussing the dietary standard and recommended intake of Mn consumption. In addition, we review some mechanisms underlying Mn-induced neurotoxicity.

Seasonal distribution of cadmium, lead, nickel, and magnesium in several tissues of mussels from the Algerian coasts

This study aims to investigate the distribution of heavy metals (Cd, Pb, Ni, and Mn) in different organs of two marine mussel species, Perna perna collected from Figuier site and Mytilus galloprovincialis sampled from Sercouf and Algiers port sites of the Algerian coast. Thirty individuals (>5 cm length) were seasonally sampled over a 1-year period from each site, and condition index (CI) and gonado somatic index (GSI) of mussels were calculated. The gill, digestive gland, rest of soft tissues, and gonad were accurately isolated and heavy metal contents were analyzed by ICP-MS. Heavy metal results, expressed on μg/g dry weight, ranged from 0.1 to 2.6 Cd, 0.1 to 17.15 Pb, 0.36 to 25.7 Ni, and 3.68 to 74.76 Mn. Thus, typical distribution of studied metals in various organs of mussels was found. In fact, the digestive gland followed by gill revealed significantly high metal concentrations. However, gonad showed low heavy metal contents. Different patterns of heavy metal distribution in various organs of mussels were found at the three sampling sites. High levels of Cd, Pb, Ni, and Mn were detected in mussels of Sercouf, Algiers port, and Figuier sites, respectively. According to the Algerian and European norms, mussels collected from all sites were healthy except those of Algiers port sampled in autumn and winter seasons where lead contamination was found.