Search

Brominated organic compounds are known as disinfection byproducts. Very recently, however, even natural brominated organic compounds (analyzed as adsorbable organic bromine; AOBr) have been found in decaying freshwater cyanobacteria blooms. Among the identified compounds was dibromoacetic acid (DBAA), which has proven to be neurotoxic at rather high concentrations in mammalian assays. Currently it is open how single compounds as well as complex mixtures impact organisms at environmentally realistic concentrations. Furthermore, it is also unclear how natural organic matter, mainly humic substances (HS), which are present in all freshwater systems, modulates the toxic impact of AOBr. Therefore, two AOBr compounds (DBAA and tetrabromobisphenol-A; TBBP-A) and AOBr-containing water samples were tested using a Caenorhabditis elegans neurotoxicity assay that measured autonomic and sensory functions. TBBP-A had an impact on three response variables of C. elegans and can be classified neurotoxic. In contrast to our expectations, DBAA led to neurostimulation of two autonomic functions, but had a temporary impact on the defecation interval. All surface water samples contained measurable amounts of AOBr. Exposure of C. elegans to concentrated water samples – one in particular – increased three of the four locomotion traits and left defecation activity and both sensory variables unchanged. This stimulation might be due to unidentified compounds in the samples or to a hormetic effect of the AOBr compounds. Thermotactic behavior was characterized by a temporary preference for the colder environment, indicating a temporary mild neurotoxicity. Overall, the set of relative simple phenotypic tests used in the current study revealed a meaningful neurotoxic or neurostimulative profile in response to chemical compounds or natural samples. Furthermore, it shows that the resulting response to natural AOBr compounds at environmentally realistic concentrations was not necessarily adverse, but instead, that the mixtures of natural AOBr were neurostimulatory. [Copyright &y& Elsevier]

During decomposition and humification of leaf litter, soil and freshwater organisms may be exposed to plant polyphenols and affected by them. If non-specific biotic interactions of these compounds were considered so far, only adverse impacts have been in the focus. Yet, potential beneficial effects remain obscure. In this contribution we followed the hydrological path of the water-soluble polyphenol, caffeic acid (CA), by testing a soil and a freshwater model animal. Caenorhabditis elegans and Moina macrocopa were exposed 0, 50, 100, 200, and 300 μM CA and lifespan and lifetime offspring output were recorded. With M. macrocopa, even 500 M were applied. In C. elegans, lifespan extension and a reduction of offspring numbers was observed; whereas M. macrocopa responded with reduced lifespan, but increased offspring numbers. Potential antimicrobial activity of CA did not apply for the lifespan extension in C. elegans. The reaction patterns of both model animals are discussed in the light of two actual hypotheses: hormesis and disposable soma theory. Hormesis can be excluded, since with both animals one life-trait parameter has been adversely affected. The disposable soma theory implies the optimal allocation of metabolic resources between somatic maintenance and reproduction. Both model organisms are r-strategists with the potential of developing diapausing stages. Hence, the different reaction patterns do not seem to be a specific optimization of the niche exploitations, but to mirror the intrinsic variability of resource allocation of different species. [ABSTRACT FROM AUTHOR]

Dissolved humic substances (HSs) are taken up by organisms and interact on various molecular and biochemical levels. With two examples, we show that HSs facilitate fish life in low pH and low calcium waters and promote longevity by mild chemical stress. We re-visit recent papers on fish adaptation in the Amazonian Rio Negro and re-interpret the results on the basis of the recent finding of gene control in the nematode Caenorhabditis elegans. In the nematode, several genes are up-regulated. This may also account for the maintenance of fish life in the Rio Negro. Exposure to HSs exerts mild chemical stress on the exposed organisms and deprives them of energy; however, the nematode C. elegans actively looks for such environments. With life-table and DNA gene filter studies we show that HSs may cause longevity and multiple stress resistance. Furthermore, we propose likely structures of the HSs responsible for these effects. [ABSTRACT FROM AUTHOR]