Browsing by Author "Sandvik, M."

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Assessment of farming practices and uses of agrochemicals in Lake Manyara basin, Tanzania
Nonga, H. E.; Mdegela, R. H.; Lie, E.; Sandvik, M.; Skaare, J. J.
Assessment of farming practices and uses of agrochemicals in Lake Manyara basin, Tanzania
(2011-05-18) Nonga, H. E.; Mdegela, R. H.; Lie, E.; Sandvik, M.; Skaare, J. J.
This study was conducted to assess farming practices, agrochemical usage and environmental pollution in Manyara basin, Tanzania. Field surveys, interviews, questionnaires and Lake Manyara nutrient analysis were used in data collection. The highest number (95%) of households grew crops, namely, maize, rice, banana and vegetables with median farm size of 3 ha. Irrigated farming was common (75%) which enhanced cultivation on same piece of land up to 6 times a year. Farmers indiscriminately used pesticides, namely, insecticides (50%), fungicides (37.5%) and herbicides (12.5%). Uses of endosulfan in vegetable farms poses public health threats to consumers. Most respondents (85%) applied insecticides in vegetables up to 4 times per cropping season. Excessive use of pesticides and haphazard disposal of pesticide remnants and containers caused environmental pollution. The average amount of acaricides used was 1109±915 ml (mean ± SD) per livestock keeper per month per. Most farmers (78%) used inorganic fertilizers and animal manure (43.4%). Low levels of ammonium (3.6±3.1 μg/L), nitrate (1±0.8μg/L) and phosphate (36.1±42 μg/L) were recorded in the lake. Easy access to agrochemicals, limited knowledge of pesticide on environmental health and limited extension services were factors for indiscriminate uses of agrochemicals. Increasing farmers awareness and training aimed at sustainable agriculture, agrochemical uses and integrated pest management is suggested.
Conjugation of microcystins with thiols is reversible: Base-catalyzed deconjugation for chemical analysis
(ACS Publications) Miles, C. O.; Sandvik, M.; Nonga, H. E.; Ballot, A.; Wilkins, A. L.; Rise, F.; Jaabaek, J. A. H.; Loader, J. I.
Conjugation of microcystins with thiols is reversible: Base-catalyzed deconjugation for chemical analysis
(Chemical Research in Toxicology) Miles, C. O.; Sandvik, M.; Nonga, H. E.; Ballot, A.; Wilkins, A. L.; Rise, F.; Jaabaek, J. A. H.; Loader, J. I.
Conjugation of microcystins with thiols is reversible: Base-catalyzed deconjugation for chemical analysis
(ACS Publications, 2016-03-21) Miles, C. O.; Sandvik, M.; Nonga, H. E.; Ballot, A.; Wilkins, A. L.; Rise, F.; Jaabaek, J. A. H.; Loader, J. I.
Microcystins are potent cyclic heptapeptide toxins found in many freshwater cyanobacteria. Most microcystins contain an α,β-unsaturated amide that can react with thiolcontaining amino acids, peptides, and proteins in vivo and in vitro. While soluble conjugates formed from small peptides can be extracted and analyzed directly by LC−MS, microcystins conjugated to proteins are analyzed after oxidative cleavage of their Adda side chains, but information on which microcystin analogues were present is lost. Observations during the development of thiol-derivatization-based LC−MS methods for microcystin analysis indicated that the reaction of thiols with microcystins was reversible. The kinetics of deconjugation was investigated with mercaptoethanol as a model thiol to identify suitable reaction conditions. A range of microcystins conjugated to mercaptoethanol, methanethiol, cysteine, and glutathione were then successfully deconjugated, demonstrating the feasibility of releasing conjugated forms of microcystins for chemical analysis. Reagents for removing the released thiols or for trapping the released microcystins increased the reaction rate. Optimization of methodologies based on this reaction should increase the method’s utility for measuring free and conjugated microcystins. The results also indicate that thiol-conjugated microcystins slowly release free microcystins, even at neutral pH, with consequences for assessment of toxin exposure, metabolism, and trophic transfer. A range of other common natural and environmental toxins, such as deoxynivalenol and acrylamide, also contain α,β-unsaturated carbonyl groups and can be expected to behave in a similar manner.
Cyanobacteria and cyanobacterial toxins in the alkaline-saline Lakes Natron and Momela, Tanzania
(African Journal Online) Nonga, H. E.; Mdegela, R. H.; Sandvik, M.; Lie, E.; Miles, C. O.; Skaare, J. U.
Dioxins, PCBs, chlorinated pesticides and brominated flame retardants in free-range chicken eggs from peri-urban areas in Arusha, Tanzania: Levels and implications for human health
(Elsevier) Polder, A.; Müller, M. B.; Brynildsrud, O.B.; de Boer, J.; Hamers, T.; Kamstra, J. H.; Lie, E.; Mdegela, R. H.; Moberg, H.; Nonga, H. E.; Sandvik, M.; Skaare, J. U.; Lyche, J. L.
Isolation of the Tephrosia vogelii extract and rotenoids and their toxicity in the RTgill-W1 trout cell line and in zebrafish embryos
(ELSEVIER) Said, A.H.; Solhaug, A.; Sandvik, M.; Msuya, F.E.; Kyewalyanga, M.S.; Mmochi, A.J.; Lyche, J.L.; Hurem, S.
LC-MS analysis with thiol derivatization to differentiate [Dhb7]- from [Mdha7]‑Microcystins: Analysis of cyanobacterial blooms, planktothrix cultures and European crayfish from lake Steinsfjorden, Norway
(American Chemical Society) Miles, C. O.; Sandvik, M.; Haande, S.; Nonga, H. E.; Ballot, A.
LC-MS analysis with thiol derivatization to differentiate [Dhb7]- from [Mdha7]‑Microcystins: Analysis of cyanobacterial blooms, planktothrix cultures and European crayfish from lake Steinsfjorden, Norway
(American Chemical Society, 2013-03-26) Miles, C. O.; Sandvik, M.; Haande, S.; Nonga, H. E.; Ballot, A.
Kinetic studies showed that [Asp3, Dhb7]MC-RR reacted with mercaptoethanol hundreds of times more slowly than MC-RR and a range of other [Mdha7]-containing microcystin congeners. The difference in reaction rate was sufficiently large that derivatization of microcystin-containing samples with mercaptoethanol, followed by LC-MS analysis, clearly discriminated between microcystins containing the isobaric [Dhb7]- and [Mdha7]-groups. Application of this approach, using LC-MS with both-ion trap and triplequadrupole mass spectrometers, to water samples and Planktothrix cultures from Lake Steinsfjorden, Norway, demonstrated the presence of [Asp3, Dhb7]MC-RR (5), [Asp3]MC-RY (14), and [Asp3]MC-LY (16), as well as analogues tentatively identified as [Asp3]MC-RR (4), [Asp3, DMAdda5, Dhb7]MC-LR (6), [Asp3, Dhb7]MC-HtyR (8), [Asp3]MC-HtyR (9), [Asp3, Dhb7]MC-LR (10), [Asp3]MC-LR (11), [Asp3, Dhb7]MC-RY (15), and [Asp3, Dhb7]MC-LY (17), together with low levels of several other analogues. This is the first use of this thiol-based LC-MS approach to identify Dhb-containing microcystins, and allowed identification of LC-MS peaks in a mixture of [Mdha7]- and [Dhb7]-congeners of [Asp3]MC-RR (4, 5), -RY (14, 15), and -LY (16, 17) in the samples from L. Steinsfjorden. This is also the first report of MC-RY-congeners outside of Africa, or in Planktothrix spp. Analysis of European crayfish (Astacus astacus) taken from L. Steinsfjorden revealed the presence of only trace levels of microcystins in the edible parts.
Levels and patterns of persistent organic pollutants (POPs) in tilapia (Oreochromis sp.) from four different lakes in Tanzania: Geographical differences and implications for human health
(Elsevier) Lie, Elisabeth; Polder, A.; Müller, M. B.; Lyche, J. L.; Mdegela, R. H.; Nonga, H. E.; Mabiki, F.; Mbise, T. J.; Skaare, J. U.; Sandvik, M.; Skjerve, E.; Lie, E.
Socio-economic values of wetland resources around lake Manyara, Tanzania: assessment of environmental threats and local community awareness on environmental degradation and their effects
(Journal of Wetlands Ecology) Nonga, H. E.; Mdegela, R. H.; Lie, E.; Sandvik, M.; Skaare, J. U.
Thiol Derivatization for LC-MS Identification of Microcystins in Complex Matrices
(ACS Publications) Miles, C. O.; Sandvik, M.; Nonga, H. E.; Rundberget, T.; Wilkins, A. L.; Rise, F.; Ballot, A.
Thiol Derivatization for LC-MS Identification of Microcystins in Complex Matrices
(ACS Publications, 2012-07-18) Miles, C. O.; Sandvik, M.; Nonga, H. E.; Rundberget, T.; Wilkins, A. L.; Rise, F.; Ballot, A.
Microcystins are a group of cyclic heptapeptides originating from cyanobacteria. Cyanobacteria also produce a range of peptides and other compounds that can result in complex chromatograms when samples are analyzed by LC-MS. Derivatization with appropriate thiols (e.g., mercaptoethanol) of the olefin in the α,β-unsaturated amide present in most microcystins was shown to simplify analysis of LC-MS chromatograms of sample extracts, making it much easier to identify peaks corresponding to candidate microcystins. Furthermore, interpretation of MS2 spectra was facilitated by addition of the mass associated with the thiol to the α,β-unsaturated amide of microcystins. Cyanotoxins containing Mdha or Dha reacted readily with thiols, whereas Mser, Ser, Mdhb, and thiol-derivatives of Mdha or Dha did not react under the conditions used. This approach therefore provides a convenient LC-MS method to obtain evidence for the presence of Mdha or Dha and can likely be used to differentiate between the isobaric amino acids Mdha and Dhb in candidate cyanotoxin peaks. When O-(2-mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (MEMHEG) (Mwt. 356) was used as the thiol, the resulting derivatives eluted in an LC-MS mass window that was largely free of interferences. This approach simplifies detection of candidate microcystin analogues even in the presence of complex mixtures of coeluting components. The method was used for qualitative analysis of a Microcystis aeruginosa culture from Lake Naivasha, Kenya, and the results were verified using precursor-ion scanning and high-resolution mass spectrometry.