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Are individual NOEC levels safe for mixtures? A study on mixture toxicity of brominated flame-retardants in the copepod Nitocra spinipes.
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
2008 (English)In: Chemosphere, ISSN 0045-6535, Vol. 72, no 9, 1242-9 p.Article in journal (Refereed) Published
Abstract [en]

In aquatic ecosystems organisms are exposed to mixtures of pollutants. Still, risk assessment focuses almost exclusively on effect characterization of individual substances. The main objective of the current study was therefore to study mixture toxicity of a common group of industrial substances, i.e., brominated flame–retardants (BFRs), in the harpacticoid copepod Nitocra spinipes. Initially, 10 BFRs with high hydrophobicity but otherwise varying chemical characteristics were selected based on multivariate chemical characterization and tested individually for effects on mortality and development using a partial life cycle test (six days) where silica gel is used as a carrier of the hydrophobic substances. Based on these findings, six of the 10 BFRs were mixed in a series of NOEC proportions (which were set to 0.008, 0.04, 0.2, 1, and five times the NOEC concentrations for each individual BFR), loaded on silica gel and tested in a full life cycle test (26 days). Significantly increased mortality was observed in N. spinipes after six and 26 days exposure at a NOEC proportion that equals the NOECLDR value (×1) for each BFR in the mixture (p = 0.0015 and p = 0.0105, respectively). At the NOEC × 5 proportion all animals were dead. None of the other NOEC proportions caused significant negative responses related to development and reproduction. This shows that low concentrations of individual substances can cause toxicity if exposed in mixtures, which highlights the need to consider mixture toxicity to a greater extent in regulatory work.

Place, publisher, year, edition, pages
2008. Vol. 72, no 9, 1242-9 p.
Keyword [en]
Environmental risk assessment, Silica gel, Crustacean, Reproduction, Development, Statistical power
URN: urn:nbn:se:umu:diva-10190DOI: doi:10.1016/j.chemosphere.2008.05.004PubMedID: 18561976OAI: diva2:149861
Available from: 2008-08-05 Created: 2008-08-05 Last updated: 2010-01-15Bibliographically approved
In thesis
1. Persistency, bioaccumulation and toxicity assessment of selected brominated flame retardants
Open this publication in new window or tab >>Persistency, bioaccumulation and toxicity assessment of selected brominated flame retardants
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Brominated flame retardants (BFRs) are chemicals used in e.g. electronic equipment, textiles and plastics for the prevention of fire. Over recent decades, concern has been raised regarding some heavily used BFRs, since the levels in the environment have been increasing. In the present thesis, persistent, bioaccumulative, and toxic (PBT) properties were studied for a structurally varied set of BFRs selected to represent more than 60 organic BFRs. The studied BFRs include: 2,4,4'-tribromodiphenyl ether (BDE 28), 2,2',3,4,4',5',6-heptabromodiphenyl ether (BDE  183), decabromodiphenyl ether (BDE 209), hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), tetrabromobisphenol A 2-hydroxyethyl ether (TBBPA OHEE), 2,4,6-tribromophenol (246BrPh), 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), and hexabromobenzene (HxBrBz).

It is likely that soil will act as a sink for BFRs. Therefore, studies of BFRs were performed on persistence in soil, and on bioaccumulation from soil in the earthworm Eisenia fetida. Large variation in the biodegradability in soil among the tested BFRs was observed. The studied brominated diphenyl ethers (BDE 28 and BDE 209) were very persistent under both aerobic and anaerobic conditions, while 246BrPh and TBECH degraded quickly in both aerobic and anaerobic soil. The bioaccumulation in earthworm from soil was high for HxBrBz, TBECH and for tested brominated diphenyl ethers with 4-6 bromine atoms (BDE 47, BDE 99, and BDE 153). Bioaccumulation was also studied in zebrafish after dietary exposure to a mixture of BFRs. It was shown that several metabolites were formed and retained in zebrafish, which highlights the importance of also searching for and identifying persistent degradation products. Maternal transfer was shown for all BFRs present in the female zebrafish. This shows that zebrafish young (fry) are exposed to these BFRs at approximately the same concentrations as female zebrafish during the early-life stages, when fish are usually most sensitive to organic contaminants. Toxicity of individual BFRs and a BFR mixture was studied in Nitocra spinipes using a silica gel-based system. Highest toxicities were observed for BDE 28, TBBPA, and TBBPA OHEE. In the mixture toxicity study, simultaneous exposure to low concentrations (individually causing no significant effect) of six BFRs significantly affected the survival of Nitocra spinipes. The results from the PBT studies presented in the thesis and literature data were compared with the criteria for PBT classification, as set in the European REACH legislation. Further, some BFRs with physico-chemical properties similar to those of identified PBTs were suggested to be prioritized for future PBT testing.

Place, publisher, year, edition, pages
Umeå: Print & Media, 2009. 57 p.
persistence, bioaccumulation, toxicity, biodegradation, biotransformation, PBT, read across, soil, earthworm, zebrafish, copepod, BFRs, polybrominated diphenyl ethers, tetrabromobisphenol A, hexabromocyclododecane, hexabromobenzene, 2, 4, 6-tribromophenol, tetrabromobisphenol A, 2-hydroxyethyl ether, 1, 2-dibromo-4-(1, 2-dibromoethyl)cyclohexane
National Category
Environmental Sciences
urn:nbn:se:umu:diva-22528 (URN)978-91-7264-805-0 (ISBN)
Kemiska institutionen, 90187, Umeå
Public defence
2009-06-05, MA121, MIT-huset, Umeå Universistet, Umeå, 10:00 (English)
Available from: 2009-05-15 Created: 2009-05-12 Last updated: 2014-03-10Bibliographically approved

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