Abstract
Harmful Algal Blooms (HABs) in freshwater systems and intensified aquaculture have increased the risk to human health through exposure to cyanotoxins such as microcystin-LR (MC-LR). To understand the uptake and processing of MC-LR in humans, the pig was chosen as an animal model. This was assessed by repeated exposure for 13 weeks of eight animals dosed daily with MC-LR at 0.04 µg/kg bw, repeated with six animals over five weeks at a dose 50 times higher at 2 µg/kg bw. An analytical method was developed for MC-LR in porcine serum and also to analyse levels of free MC-LR in harvested porcine tissues, with Lemieux Oxidation employed to determine bound MC-LR in these tissues. MC-LR was not detected in the serum of treated animals from either experiment but free MC-LR was observed in the large intestine and kidney from two animals from the higher dosed group at levels of 1.4 and 1.9 µg/kg dry weight (dw) respectively. The results indicated 50% of higher dosed animals accumulated bound MC-LR in liver tissue, averaging 26.4 µg, approximately 1.1% of the dose administered. These results point to the potential uptake and accumulation of MC-LR in human liver tissue exposed chronically to sub-acute doses.
Highlights
Harmful Algal Blooms (HABs) are increasing in number and severity in freshwater systems globally with these HABs caused by certain cyanobacterial species growing exponentially and producing secondary metabolites called cyanotoxins
As the MC-LR used in the validation was not a Certified Reference Material (CRM) and as the MC-LR may not act as it does in a real sample, EC directive 2002/657 states that at the spiking level used of 5 ppb (5 ng/ml serum), the minimum trueness has to be in the range −30% to +10%
A further UPLC-MS/MS method was developed for the extraction and analysis of free MC-LR
Summary
Harmful Algal Blooms (HABs) are increasing in number and severity in freshwater systems globally with these HABs caused by certain cyanobacterial species growing exponentially and producing secondary metabolites called cyanotoxins. Rising global temperatures caused by climate change is predicted to play an increasing role in the future[4], with higher water temperatures known to promote surface-forming HABs. Approximately 40 cyanobacterial species are capable of producing cyanotoxins[5,6] with the most studied being the hepatotoxic microcystins (MCs), of which around 130 different congeners have been characterised[7]. Microcystin-LR (MC-LR), with amino acids leucine (L) and arginine (R) at positions 2 and 4 respectively[8], is the most studied and acutely toxic and is listed as one of the most important algal toxins in the United States[9]. Due to its toxicity and based on the No Observable Adverse Effect Level (NOAEL) value of 40 μg/kg body weight in the 13 week drinking water study carried out in mice with MC-LR (Fawell et al 1994), the World Health Organisation (WHO) established a 1 μg/L (free plus cell-bound) guideline value for drinking water and a Tolerable Daily Intake (TDI) of 0.04 μg/kg body weight per day for MC-LR in contaminated seafood[11]
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