Leo Goeyens

A review of dietary and non-dietary exposure to bisphenol-A.

Due to the large number of applications of bisphenol-A (BPA), the human exposure routes are multiple. We aimed to review shortly the food and non-food sources of BPA, and to evaluate their contribution to the human exposure. Food sources discussed here include epoxy resins, polycarbonate and other applications, such as paperboard and polyvinylchloride materials. Among the non-food sources, exposures through dust, thermal paper, dental materials, and medical devices were summarized. Based on the available data for these exposure sources, it was concluded that the exposure to BPA from non-food sources is generally lower than that from exposure from food by at least one order of magnitude for most studied subgroups. The use of urinary concentrations from biomonitoring studies was evaluated and the back-calculation of BPA intake seems reliable for the overall exposure assessment. In general, the total exposure to BPA is several orders of magnitude lower than the current tolerable daily intake of 50 μg/kg bw/day. Finally, the paper concludes with some critical remarks and recommendations on future human exposure studies to BPA.

Are potential sources for human exposure to bisphenol-A overlooked?

This review summarizes the numerous applications of bisphenol-A (BPA) and the potential sources for human exposure. The exposure to humans is believed to occur mainly through food contamination from polycarbonate bottles, as well as through food and beverage cans coated with epoxy resins. However, there seems to be a discrepancy between exposure assessments based on biomonitoring data and those based on food/drink concentrations. Several recent studies indicated also the importance of non-food sources. Although the main use of BPA is polymerization to polycarbonate and epoxy resins, it can also be used as an additive, from which it may be easily released. Several studies have already provided scientific evidence for the contribution of sources for dermal BPA absorption, such as thermal paper where BPA is used as an additive. Polymeric applications of BPA require further investigation regarding the amounts of BPA present, as well as the factors affecting its release and potential dermal or non-dermal exposure from these sources. It is clear that not all sources of BPA have been identified. This overview emphasizes the necessity to study also the exposure to these unexpected sources of BPA.

Barite formation in the Southern Ocean water column

Abstract The intensity of past biological activity can be correlated with the occurrence of suspended and sedimented barite (BaS04). To date, there is a lack of information on the processes controlling the production of pelagic barite. During the EPOS-2 cruise (November–December 1988 ), situated in the Scotia Sea-Weddell Sea Confluence, suspended matter samples were taken for analysis of total Ba by inductively coupled plasma-atomic emission spectroscopy ( ICP-AES ) and for scanning electron microscopy-electron microprobe (SEM-EMP). The vertical profiles of particulate barium generally show a Ba maximum between 200 and 500 m. SEM-EMP investigations on Scotia-Weddell Sea Confluence profiles provide a possible explanation for the origin of this subsurface Ba maximum. In the surface waters (i.e. above 200 m) barite is mainly contained within large bioaggregates. The fact that in the first 10–20 m of the water column the barite particles in the bioaggregates appear as amorphous entities without a clear crystalline habit (in contrast to their form at greater depths) probably reflects the evolution from BaSO 4 precipitation to barite crystallization. Below this surface layer barite in bioaggregates is present as microparticles with a crystalline habit. Deeper in the water column, below the first few hundred meters, barite crystals occur as free discrete particles. This suggests that in the subsurface zone (below 200 m) the “aggregates” are dispersed, possibly as a result of bacterial activity on the organic matrix, thereby releasing the individual barite crystals. As these microcrystals, set free in the water column, settle much more slowly than the carrier-aggregate and as barite dissolves relatively slowly, local accumulation of barite can result. In some cases high Ba concentrations are present in the first 10–20 m of the water column, occasionally coinciding with biomass parameter maxima. This correlation suggests active precipitation by the living phytoplankton cell (i.e. intravacuolar barite formation), as already observed by others for cultures of marine algae (Pavlovales). Our SEM-EMP investigations on INDIGO 3 and EPOS-2 samples did not reveal any association of barite with identifiable phytoplankton individuals. Thus, SEM-EMP evidence favours passive precipitation in saturated microenviron-ments as the process involved in formation of pelagic barite.

ACCUMULATION OF SUSPENDED BARITE AT MESOPELAGIC DEPTHS AND EXPORT PRODUCTION IN THE SOUTHERN OCEAN

The relation between the accumulation of barite (BaSO4) microcrystals in suspended matter from the mesopelagic depth region (100 to 600 meters) and the type of production in the euphotic layer (new versus recycled) was studied for different Southern Ocean environments. Considerable subsurface barite accumulated in waters characterized by maintained new production and limited grazing pressure during the growth season. On the other hand, little if any barite accumulated in areas where relatively large amounts of photosynthetically fixed carbon were transferred to the microheterotrophic community and where recycled production became predominant.

Suspended barite as a tracer of biological activity in the Southern Ocean

Abstract During two cruises in the Southern Ocean (INDIGO 3, Indian sector and EPOS 2, Scotia-Weddell Confluence) suspended matter samples were collected for analysis of several biogenic elements including Ba, Si and particulate organic carbon (POC). The good agreement between particulate barium in subsurface water with oxygen minimum concentrations as well as with nitrate depletions suggests that it reflects the intensity of new production over the past season. As a consequence of new production in the Southern Ocean being performed mainly by diatoms, the occurrences of barite and diatoms are related in the water column. In areas characterized by diatom-poor phytoplankton, barite does occur, but in lower concentrations.

Nutrient anomalies in Fragilariopsis kerguelensis blooms, iron deficiency and the nitrate/phosphate ratio (A. C. Redfield) of the Antarctic Ocean

Abstract During seasonal development of blooms in the Polar Frontal region, concentrations of nitrate and phosphate decreased in surface waters. In blooms of Fragilariopsis kerguelensis at the southern rim (49–50°S) of the Polar Frontal region the dissolved ratio NO 3 PO 4 increased from the winter value of ∼14 to 15.8 (18 October 1992) to as high as 25 (23 November 1992). Ambient dissolved Fe in these blooms was subnanomolar compared to ∼1.1–1.9 nM in the overall Polar Frontal region. Blooms more northerly in the Polar Frontal region were dominated by other diatoms and higher dissolved Fe (> 1 nM), and showed only very modest NO 3 PO 4 anomalies. From nutrient inventories the biogenic pools (PON and DON) and export of settling biogenic debris would have N P ratios as low as 4.4–6.1 compared to ∼14 in deep Antarctic waters. Such shifts are consistent with decreasing availability of Fe for nitrate reduction, but also may be due to intrinsically low N P in Fragilariopsis kerguelensis cells. Moreover, a low ratio DON DOP in dissolved organic matter and enhanced recycling of N versus P cannot be excluded either. Triplicate mesocosm (20 l) experiments were performed with a diatom-dominated community in ambient seawater (initial Fe = ∼0.9 nM) collected at the Polar Front during early spring. Three other triplicates were enriched with 2 nM Fe to total Fe ∼ 2.9 nM. During the incubations, the Fe-enriched experiments showed assimilation at near-perfect Redfield N P ratios of ∼15 and a virtually near-zero intercept. The untreated incubations showed significantly lower uptake ratios at ∼13 and non-zero intercepts, suggesting leftover nitrate after all phosphate was utilised. At initial Fe = ∼0.9 nM, the Fe-containing algal enzymes for reduction of nitrate appeared to be impaired, hence nitrate assimilation was less efficient. The observed N P fractionation in Fragilariopsis kerguelensis blooms at the Polar Frontal region, in combination with the local formation of AAIW flowing northward, might help maintain the lower N P ratio at ∼14 in Antarctic waters, as compared to a ∼15 as an average value for the other oceans. The functionality of Fe in C-fixation, nitrate assimilation as well as N2 fixation may partly explain the large variability of the NO 3 PO 4 ratio in this and other ocean basins (Fanning, 1992; Journal of Geophysical Research, 97, 5693–5712), as well as recently reported variations in the extended C/N/P ratio.

Iron enrichment experiments in the Southern Ocean: physiological responses of plankton communities

The physiological responses of plankton to iron enrichment were investigated in experiments performed in 20-1 culture vessels. Natural phytoplankton communities in sea water, with mean ambient Fe concentrations ranging from 0.3-0.4 nM in the Antarctic Circumpolar Current to 1.2-1.9 nM in the Polar Frontal region, were incubated for several days. Upon addition of 2 nM of iron, synthesis of chlorophyll a and nutrient uptake was stimulated. The specific nitrate-uptake rates as determined by 15N-uptake experiments consistently increased, as well as the ratios of chlorophyll a to particulate carbon. Growth rates in iron-enriched bottles were consequently enhanced relative to control bottles. The biochemical composition of the plankton community, indicated by carbon to nitrogen ratios and fatty acid composition, remained unaffected by iron addition. On the basis of 14C incorporation into the major biochemical pools, no changes were observed in the allocation of carbon into proteins, polysaccharides, lipids and low-molecular-weight metabolites in the particulate fraction. Antarctic phytoplankton endures the low ambient iron concentrations by maintaining physiological processes at lower activity rates, whereas the biochemical composition of the plankton remains virtually unaffected.

Particulate barium stocks and oxygen consumption in the Southern Ocean mesopelagic water column during spring and early summer: Relationship with export production

Abstract Particulate barium was analysed in the upper 600 m of the Southern Ocean water column during repeated transects along the 6°W meridian in October–November 1992. The transects extended between the northern edge of the Weddell Gyre (57°30′S) in the south to 47°S within the Polar Front Zone (PFZ) in the north. From earlier studies, it is known that the largest fraction of Ba in oceanic suspended matter occurs as barite micro-crystals. In the PFZ, an increase in the particulate Ba content in surface waters and at mesopelagic depths can be significant over the investigation period (1 month) and follows the increase of primary production during bloom development. Using an inverse one-dimensional advection-diffusion-consumption model, O2 consumption between the base of the mixed layer and 1000 m was estimated. The shapes of the vertical particulate Ba profiles are very similar to those of calculated O2 consumption rates, emphasizing the close link between organic matter oxidation and Ba-barite release at a mesopelagic depth. For the southern Antarctic Circumpolar Current (ACC), depth-integrated rates of O2 consumption correlate significantly with primary production and mesopelagic particulate Ba concentration. For the PFZ, these relationships are subject to more speculation since this is a region of intense mixing, and the appropriate value of the turbulent diffusion coefficient is uncertain. For the ACC, the observed relationship presents the possibility of defining a transfer function between export production to the mesopelagic depth zone and mesopelagic Ba accumulation. The observed regression between rate of O2 consumption and primary production in the southern ACC suggests that about 10% of the synthesized organic carbon can be oxidized in the upper 1000 m of the water column.

Export production in the Bay of Biscay as estimated from barium – barite in settling material: a comparison with new production

We present barium data for sediment traps deployed in a northeast Atlantic margin environment (Bay of Biscay). Fluxes of excess barium were measured with the objective of calculating carbon export production rates from the surface mixed layer and thus contribute to the understanding of organic carbon transport in a margin environment. Therefore, it was necessary to properly understand the different processes that affected the barium fluxes in this margin environment. Seasonal variability of POC/Ba flux ratios and decrease of barium solubilisation in the trap cups with increasing depth in the water column probably indicate that the efficiency of barite formation in the organic micro-environment varies with season and that the process is relatively slow and not yet completed in the upper 600 m of water column. Thus barite presence in biogenic aggregates will significantly depend on water column transit time of these aggregates. Furthermore, it was observed that significant lateral input of excess-Ba can occur, probably associated with residual currents leaving the margin. This advected excess-Ba affected especially the recorded fluxes in the deeper traps (>1000 m) of the outer slope region. We have attempted to correct for this advected excess-Ba component, using Th (reported by others for the same samples) as an indicator of enhanced lateral flux and assigning a characteristic Ba/Th ratio to advected material. Using transfer functions relating excess-Ba flux with export production characteristic of margin areas, observed Ba fluxes indicate an export production between 7 and 18 g C m−2 yr−1. Such values are 3–7 times lower than estimates based on N-nutrient uptake and nutrient mass balances, but larger and more realistic than is obtained when a transfer function characteristic of open ocean systems is applied. The discrepancy between export production estimates based on excess-Ba fluxes and nutrient uptake could be resolved if part of the carbon is exported as dissolved organic matter. Results suggest that margin systems function differently from open ocean systems, and therefore Ba-proxy rationales developed for open ocean sites might not be applicable in margin areas.

Brominated flame retardants in Belgian home-produced eggs: Levels and contamination sources

The extent and the sources of contamination with brominated flame retardants (BFRs), such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD), in home-produced eggs from free-foraging chicken of Belgian private owners were investigated. Various factors, such as seasonal variability, exposure of chickens through diet (kitchen waste) and soil, and elimination of BFRs through eggs and faeces were assessed. PBDEs were more important than HBCD in terms of concentrations and detection frequency. Concentrations of PBDEs and HBCD in Belgian home-produced eggs were relatively low and comparable with reported levels from other European countries and the US. The concentrations of PBDEs (sum of 13 congeners, including BDE 209) ranged between not detected and 32 ng/g lipid weight (lw), with medians of 3.0 and <2.0 ng/g lw for the autumn 2006 and spring 2007 campaigns, respectively. When present, BDE 209 was the major PBDE congener (45% of sum PBDEs). When BDE 209 was not detected, the PBDE profile was composed of PentaBDE (BDE 99 and BDE 47), with, in some cases, higher contribution of OctaBDE (BDE 183 and BDE 153). HBCD was also detected (<0.4 and 2.9 ng/g lw for the autumn 2006 and spring 2007 campaigns, respectively), but at lower detection frequency. The highest HBCD value was 62 ng/g lw. The similarity between profiles and seasonal variations in the concentrations of BFRs in soil and eggs indicate that soil is an important source, but not the sole source, for eggs laid by free-foraging chicken. The contamination of eggs with PBDEs and HBCD appears to be of low concern for public health and the contribution of eggs to the total daily intake of PBDEs appears to be limited (10% for chicken owners and 5% for the average Belgian consumer).