Microcystins (MCs) are hepatotoxins, produced by various species of cyanobacteria, whose occurrence is increasing worldwide owing to climate change and anthropogenic activities. More than 100 variants have been reported, and among them MC-LR is the most extensively studied, but there are other MC congeners that deserve to be investigated. The need for data to characterize the toxicological profile of MC variants other than MC-LR has been identified in order to improve risk assessment in humans and wildlife. Accordingly, the aim of this study was to evaluate the information available in the scientific literature dealing with MC-RR, as this congener is the second most common cyanotoxin in the environment. The review focuses on aspects such as occurrence in water and food, and toxicity studies both in vitro and in vivo. It reveals that, although MC-RR is a real hazard with a high exposure potential in some countries, little is known yet about its specific toxicological properties that differ from those of MC-LR, and important aspects such as genotoxicity and chronic effects have not yet been sufficiently addressed.

Microcystin (MC), a hepatotoxin that can adversely affect human health, has become more prevalent in freshwater ecosystems worldwide, owing to an increase in toxic cyanobacteria blooms. While consumption of water and fish are well-documented exposure pathways of MCs to humans, less is known about the potential transfer to humans through consumption of vegetables that have been irrigated with MC-contaminated water. Likewise, the impact of MC on the performance of food crops is understudied. To help fill these information gaps, we conducted a controlled laboratory experiment in which we exposed lettuce, carrots, and green beans to environmentally relevant concentrations of MC-LR (0, 1, 5, and 10μg/L) via two irrigation methods (drip and spray). We used ELISA and LC-MS/MS to quantify MC-LR concentrations and in different parts of the plant (edible vs. inedible fractions), measured plant performance (e.g., size, mass, edible leaves, color), and calculated human exposure risk based on accumulation patterns. MC-LR accumulation was positively dose-dependent, with it being greater in the plants (2.2–209.2μg/kg) than in soil (0–19.4μg/kg). MC-LR accumulation varied among vegetable types, between plant parts, and between irrigation methods. MC-LR accumulation led to reduced crop growth and quality, with MC-LR persisting in the soil after harvest. Observed toxin accumulation patterns in edible fractions of plants also led to estimates of daily MC-LR intake that exceeded both the chronic reference dose (0.003μg/kg of body weight) and total daily intake guidelines (0.04μg/kg of body weight). Because the use of MC-contaminated water is common in many parts of the world, our collective findings highlight the need for guidelines concerning the use of MC-contaminated water in irrigation, as well as consumption of these crops.

Department of Geography and Environmental Sciences | Department of Geography and Environmental Sciences | Globally, the occurrence of cyanobacterial blooms in freshwater ecosystems has become a concern. Cyanobacteria produces secondary metabolites, known as cyanotoxins that cause acute and chronic poisoning in animals and humans. History of mining, industrial activities and poor maintenance of wastewater treatment infrastructure are the main causes of the hyper-eutrophic conditions affecting most dams in South Africa. The co-occurrence of multiple stressors in agricultural waters and soils potentially pose a human and animal risk if contaminated water and plants are ingested. The study investigated the co-existence of cyanotoxins, anionic surfactants and metal species in irrigation water, agricultural soils and food crops and determine the health risks associated with consuming cyanotoxins contaminated plants in the Crocodile (West) Marico Water Management Area, which covers parts of Gauteng and Northwest Provinces. Lastly, the study assessed the applicability of passive sampling technology in monitoring of cyanotoxins using DIAON HP20 resins as an adsorbent. Water, food crops and soil samples were collected from Roodeplaat and Hartbeespoort dam sites in irrigation canals and cropping fields in June 2019, September 2019, February 2020, and March 2021. Seven sites were selected for sampling of water for cyanotoxins, anionic surfactants and toxic metals, while 4 farmland sites were selected for agricultural soils and food crops in Roodeplaat and Hartbeespoort sites. Physicochemical parameters of the irrigation water (pH, temperature, EC, TDS, DO), chlorophyll-a and dissolved nutrients were also monitored using Spectrophotometer and Spectro-Quant® Merck Pharo 100 with the photo-metric test kits from Merck, respectively. The levels of Microcystins (MCs), anionic surfactants, and metals were detected and quantified using the ELISA method, anionic surfactant portable photometer and inductively coupled plasma mass spectrometry (ICP- MS), respectively. The results are presented for each chapters below. The results for chapter 1 revealed the co-existence of cyanotoxins, metal species and anionic surfactants in the irrigation water, and agricultural soils, across sampling sites, throughout sampling period. The microcystins in irrigation water ranged from 0.00 to 15.57 μg/L. Total anionic surfactants in irrigation water and agricultural soil ranged from 0.01 to 3.49 mg/L and 1.81 to 5.46 mg/kg, respectively. Among all the physicochemical parameters only pH (p = 0.624), TDS (p = - 0.466), EC (p = - 0.445), and turbidity (p = 0.521) correlated with MCs. Moreover, total anionic surfactant showed to have positive moderate relationship with levels of MCs in irrigation water (p = 0.342). Metal species in irrigation water were decreased in the following order: Al > Mn > Fe > B > Zn > Ni > Cu > Pb > Cr > As and were all below the maximum DWAF acceptable limit, implying that the water was safe for irrigation use. Metal species in other soil sampling sites such as 16534.61 – 33285 mg/kg (Fe), 111.25 – 723.4 mg/kg (Cr),4.44 – 23.93 mg/kg (Pb), 0.80 – 9.70 mg/kg (As), 22.11 – 33.95 mg/kg (Cu), and 33.70 – 85.885 mg/kg (Ni) were above the maximum limit set by DEA, USEPA, and FAO/WHO for agricultural use. Thus, soils from Roodeplaat and Hartbeespoort farmland sites are contaminated by the mentioned metals. The findings from the second chapter of results revealed the bio-accumulation of microcystins and metals in food crops. The estimated daily intake (EDI) for MCs in all food crops for both adults and children were below 0.04 μg/kg DW acceptable value set by World Health Organisation, implying that the crops were safe for human consumption by adult and children population. Metal species levels accumulated in plant samples collected from different sampling sites, showed that 0.21 to 10.80 mg/kg (Cr), 19.64 to 734.00 mg/kg (Fe), 5.45 to 76.80 mg/kg (Zn), 0.01 to 0.20 mg/kg (As), 0.96 to 60.40 mg/kg (Cu), and 0.10 to 0.70 mg/kg (Pb) were above the EU and FAO/WHO guideline standards. Spearman correlation between metals in plants and water showed that only Pb (p = 0.874) and As (p = 0.809) in irrigation water had a positive moderate association with metals in plants collected from the sampling sites. The estimated daily intake (EDI) of metals via consumption of the crops were found to be below the maximum tolerable daily intake (MTDI) proposed for each metal. The translocation factors (TF) showed that only Cu and Cd were rapidly transported to the plant’s edible parts from the soil. Moreover, target hazard quotient (THQ) for each metal were below 1, indicating that consuming the food crops wont cause carcinogenic effect to the adult population, while hazard index (HI) for other sites was found to be >1 for crop plants, thus plants from these sites pose a health hazards to adult population. In addition, the target cancer risk (TCR) value for Cr and Ni in crops from other sampling sites were above the maximum threshold implying that there is a potential cancer risk to adult population over a long-term. In addition, findings from the third chapter showed that SPATT was applicable in monitoring and detecting MCs across all sampling sites and sampling months. The MCs levels in grab and SPATT bags ranged from 0.14 to 13.03 μg/L and 0.99 to 2.28 ng/g resin throughout the sampling sites and months, respectively. Thus, showing the persistence of MCs in canals and farm dams of Roodeplaat and Hartbeespoort. A spearman correlation revealed that pH (p = 0.776), Turbidity (p = 0.699) and DO (p = 0.829) had a significant positive association with total toxins in grab samples, while total dissolved MCs in SPATT samples showed negative moderate relationship with TDS (p = - 0.615) and EC (p = - 0.602). Total toxin concentrations in SPATT bags and Grab samples did not show any correlation this is because SPATT bags detect and collect microcystins within water column overtime, unlike point (Grab sampling), hence, there is no relationship between the two-sampling method. Overall results showed that SPATT bags with DIAON HP20 resin as an adsorbent proved to be applicable in monitoring and detecting microcystins in the irrigation water of Roodeplaat and Hartbeespoort sites. | NRF

β-N-Methylamino-l-alanine (BMAA) is a neurotoxin originally found in cycad seeds and now known to be produced by many species of freshwater and marine cyanobacteria. We developed a method for its determination in blue-green algae (BGA) food supplements, freshwater fish, and bottled water by using a strong cation-exchange, solid-phase extraction column for cleanup after 0.3 M trichloroacetic acid extraction of BGA supplements and fish. Bottled water was applied directly onto the solid-phase extraction column. For analysis of carbonated water, sonication and pH adjustment to 1.5 were needed. To determine protein-bound BMAA, the protein pellet left after extraction of the BGA supplement and fish was hydrolyzed by boiling with 6 M hydrochloric acid; BMAA was cleaned up on a C18 column and a strong cation-exchange, solid-phase extraction column. Determination of BMAA was by liquid chromatography of the fluorescent derivative formed with 9-fluorenylmethyl chloroformate. The method was validated by recovery experiments using spiking levels of 1.0 to 10 μg/g for BGA supplements, 0.5 to 5.0 μg/g for fish, and 0.002 μg/g for bottled water; mean recoveries were in the range of 67 to 89% for BGA supplements and fish, and 59 to 92% for bottled water. Recoveries of BMAA from spiked extracts of hydrolyzed protein from BGA supplements and fish ranged from 66 to 83%. The cleanup developed provides a useful method for surveying foods and supplements for BMAA and protein-bound BMAA.