Arsenic speciation in low-trophic marine food chain - An arsenic exposure study on microalgae (Diacronema lutheri) and blue mussels (Mytilus edulis L.)

Microalgae and blue mussels are known to accumulate undesirable substances from the environment, including arsenic (As). Microalgae can biotransform inorganic As (iAs) to organoarsenic species, which can be transferred to blue mussels. Knowledge on As uptake, biotransformation, and trophic transfer is important with regards to feed and food safety since As species have varying toxicities. In the current work, experiments were conducted in two parts: (1) exposure of the microalgae Diacronema lutheri to 5 and 10 μg/L As(V) in seawater for 4 days, and (2) dietary As exposure where blue mussels (Mytilus edulis L.) were fed with D. lutheri exposed to 5 and 10 μg/L As(V), or by aquatic exposure to 5 μg/L As(V) in seawater, for a total of 25 days. The results showed that D. lutheri can take up As from seawater and transform it to methylated As species and arsenosugars (AsSug). However, exposure to 10 μg/L As(V) resulted in accumulation of iAs in D. lutheri and lower production of methylated As species, which may suggest that detoxification mechanisms were overwhelmed. Blue mussels exposed to As via the diet and seawater showed no accumulation of As. Use of linear mixed models revealed that the blue mussels were gradually losing As instead, which may be due to As concentration differences in the mussels' natural environment and the experimental setup. Both D. lutheri and blue mussels contained notable proportions of simple methylated As species and AsSug. Arsenobetaine (AB) was not detected in D. lutheri but present in minor fraction in mussels. The findings suggest that low-trophic marine organisms mainly contain methylated As species and AsSug. The use of low-trophic marine organisms as feed ingredients requires further studies since AsSug are regarded as potentially toxic, which may introduce new risks to feed and food safety.

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.

Arsenic species in mesopelagic organisms and their fate during aquafeed processing

A responsible harvest of mesopelagic species as aquafeed ingredients has the potential to address the United Nations Sustainable Development Goal 14, which calls for sustainable use of marine resources. Prior to utilization, the levels of undesirable substances need to be examined, and earlier studies on mesopelagic species have reported on total arsenic (As) content. However, the total As content does not give a complete basis for risk assessment since As can occur in different chemical species with varying toxicity. In this work, As speciation was conducted in single-species samples of the five most abundant mesopelagic organisms in Norwegian fjords. In addition, As species were studied in mesopelagic mixed biomass and in the resulting oil and meal feed ingredients after lab-scale feed processing. Water-soluble As species were determined based on ion-exchange high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). This was supplemented by extracting arsenolipids (AsLipids) and determining total As in this fraction. The non-toxic arsenobetaine (AB) was the dominant form in mesopelagic crustaceans and fish species, accounting for approximately 70% and 50% of total As, respectively. Other water-soluble species were present in minor fractions, including carcinogenic inorganic As, which, in most samples, was below limit of quantification. The fish species had a higher proportion of AsLipids, approximately 35% of total As, compared to crustaceans which contained 20% on average. The feed processing simulation revealed generally low levels of water-soluble As species besides AB, but considerable fractions of potentially toxic AsLipids were found in the biomass, and transferred to the mesopelagic meal and oil. This study is the first to report occurrence data of at least 12 As species in mesopelagic organisms, thereby providing valuable information for future risk assessments on the feasibility of harnessing mesopelagic biomass as feed ingredients.