Relative importance of the trophic and direct pathways on PCB contamination in the rotifer species Brachionus calyciflorus (Pallas)

peer reviewedTo determine the contribution of food ingestion (trophic pathway) to PCB contamination of zooplankton in the river Meuse (Belgium), we used 14 C-labelled algae (Dictyosphaerium ehrenbergianum) to measure ingestion and assimilation rates in the rotifer species Brachionus calyciflorus . When the concentration of algae in the culture medium varied from 20 103 to 200 103 algal cells ml -1 (0.12 to 1 .18 mg C 1 - '), the Brachionus calyciflorus ingestion rate varied from 0 .25 ± 0 .12 to 1 .52 ± 0 .43 ng C ind -1 h-1 at 15 °C and from 0 .74 ± 0 .17 to 5 .93 ± 0.61 ng Cind-' h-1 at 20 °C . The assimilation efficiency (ratio of the assimilation rate to the ingestion rate) measured in a culture medium containing 200 103 algal cells ml`' was 55 .7 ± 5.8%. Since the PCB concentration measured in the phytoplankton of the river Meuse is about 3 pg PCBs g -1 D.W., the estimated PCB contamination of zooplankton ascribable to the trophic pathway ranges from 0 .22 ± 0 .17 to 1 .31 ± 0.77 jag PCBs g -1 D.W. at 15 °C and from 0.64 ± 0 .34 to 5 .10 ± 2 .10 pg PCBs g -1 D. W. at 20'C . The lower figure based on measurements effected at 20 ° C is comparable to the actual level measured in zooplankton samples collected in the river Meuse (0 .69 ± 0.20 pg PCBs g`' D.W.) . The applicability of the formula used in our estimate was checked in a 48-hour in vitro experiment in which the rotifers were fed contaminated algae . The PCB accumulation measured in the rotifers was found to coincide with the calculated PCB contamination . Additional experiments were carried out to determine the contribution of the direct pathway to PCB contamination of zooplankton living in the river Meuse (0.02 pg PCBs 1-1 of water; average dissolved organic matter : 3 mg C 1 -1 ). The PCB concentration in zooplankton resulting from direct uptake of PCBs from the water was estimated at 0 .19 ± 0.05 jug PCBs g -1 D.W. These results show that in zooplankton living in polluted ecosystems, PCBs are likely to accumulate via the trophic pathway to concentrations up to 30 times higher than by direct contamination . Furthermore, our estimates of PCB contamination via the trophic pathway coincide quite well with actual concentrations measured in situ

Cowries in the archaeology of West Africa: the present picture

Despite the perceived importance of cowrie shells as indicators of long-distance connections in the West African past, their distribution and consumption patterns in archaeological contexts remain surprisingly underexplored, a gap that is only partly explicable by the sparse distribution of archaeological sites within the sub-continent. General writings on the timeline of importation of cowries into West Africa often fail to take into account the latest archaeological evidence and rely instead on accounts drawn from historical or ethnographic documents. This paper is based on a first-hand assessment of over 4500 shells from 78 sites across West Africa, examining chronology, shell species and processes of modification to assess what distribution patterns can tell us about the history of importation and usage of cowries. These first-hand analyses are paralleled by a consideration of published materials. We re-examine the default assumption that two distinct routes of entry existed — one overland from North Africa before the fifteenth century, another coming into use from the time sea links were established with the East African coast and becoming predominant by the middle of the nineteenth century. We focus on the eastern part of West Africa, where the importance of imported cowries to local communities in relatively recent periods is well known and from where we have a good archaeological sample. The conclusion is that on suitably large assemblages shell size can be an indication of provenance and that, while the present archaeological picture seems largely to confirm historical sources, much of this may be due to the discrepancy in archaeological data available from the Sahara/Sahel zone compared to the more forested regions of the sub-continent. Future archaeological work will clarify this matter

Hunter–gatherer mobility and technological landscapes in southernmost South America: a statistical learning approach

The present work aims to quantitatively explore and understand the relationship between mobility types (nautical versus pedestrian), specific technological traits and shared technological knowledge in pedestrian hunter–gatherer and nautical hunter–fisher–gatherer societies from the southernmost portion of South America. To that end, advanced statistical learning techniques are used: state-of-the-art classification algorithms and variable importance analyses. Results show a strong relationship between technological knowledge, traits and mobility types. Occupations can be accurately classified into nautical and pedestrian due to the existence of a non-trivial pattern between mobility and a relatively small fraction of variables from some specific technological categories. Cases where the best-fitted classification algorithm fails to generalize are found significantly interesting. These instances can unveil lack of information, not enough entries in the training set, singular features or ambiguity, the latter case being a possible indicator of the interaction between nautical and pedestrian societies.HAR-2009-06996, CSD2010-00034, HAR2017- 90883-REDC, CULM-HAR2016-77672-P (Ministerio de Ciencia e Innovacio´n de Espan˜ a); PIP-0706, PIP-0348 (Consejo Nacional de Investigaciones Cientı´ficas y Tecnolo´gicas-Argentina) and PICT 2012-2148 (Ministerio de Ciencia, Tecnologı´a e Innovacio´n Productiva de la Repu´ blica Argentina); PROC/12-120610-A (SESAR WPE Long Term and Innovative Research-European Commission); and Project GR-7846 (Wenner-Gren Foundation for Anthropological Research

Back to the Grindstone? The Archaeological Potential of Grinding-Stone Studies in Africa with Reference to Contemporary Grinding Practices in Marakwet, Northwest Kenya

This article presents observations on grinding-stone implements and their uses in Elgeyo-Marakwet County, northwest Kenya. Tool use in Marakwet is contextualized with a select overview of literature on grinding-stones in Africa. Grinding-stones in Marakwet are incorporated not only into quotidian but also into more performative and ritual aspects of life. These tools have distinct local traditions laden with social as well as functional importance. It is argued that regionally and temporally specific studies of grinding-stone tool assemblages can be informative on the processing of various substances. Despite being common occurrences, grinding-stone tools are an under-discussed component of many African archaeological assemblages. Yet the significance of grinding-stones must be reevaluated, as they hold the potential to inform on landscapes of past food and material processing

GRAZING OF BOSMINA LONGIROSTRIS ON TWO PLANKTONIC ALGAE: THE INFLUENCE OF SIZE AND TASTE.

The cladoceran Bosmina longirostris is a dominant species in the River Meuse (Belgium) especially during summer. Grazing of this small-sized cosmopolitan cladoceran on algae has been stated to be related to the size of the grazed cells by some authors while other studies emphasised on the ability of bosminids to actively capture 'good tasting' particles. Grazing experiments were carried out in the laboratory with B. longirostris feeding on two algal species (Dictyosphaerium ehrenbergianum, 3-4 µm of diameter, and Chlamydomonas reinhardtii, 9-10 µm of diameter). Gut passage times and ingestion rates of the bosminids were determined with radioactively and fluorescently labelled algae. Although both algae have sizes reported to be actively grazed by B. longirostris, they were ingested at very different rates. The relative influence of cell size and cell 'taste' will be discussed

Laboratory and in situ grazing rates of freshwater rotifers and their contribution to community grazing rates

peer reviewe