Jan Arie Vonk

How to assess exposure of aquatic organisms to manufactured nanoparticles

Ecological risk of chemicals is measured by the quotient of predicted no-effect concentrations and predicted exposure concentrations, which are hard to assess for manufactured nanomaterials (NMs). This paper proposes modifications to currently used models, in order to make them suitable for estimating exposure concentrations of NMs in the aquatic environment. We have evaluated the adequacy of the current guidance documents for use with NMs and conclude that nano-specific fate processes, such as sedimentation and dissolution need to be incorporated. We have reviewed the literature on sedimentation and dissolution of NMs in environmentally relevant systems. We deduce that the overall kinetics of water-sediment transport of NMs should be close to first order. The lack of data on dissolution of NMs under environmentally realistic conditions calls for a pragmatic decision on which rates to be used in modeling. We find that first order removal kinetics for dissolution seems adequate. Based on limited data from literature, probable removal rates range from 0 to 10(-4)s(-1) for sedimentation, and from 0 to 10(-5)s(-1) for dissolution. Further experimental data at environmentally relevant conditions for sedimentation and dissolution of NMs is needed.

The biology of Thalassia: paradigms and recent advances in research

The two species belonging to the genus Thalassia (Family: Hydrocharitaceae), T. testudinum Banks ex Konig and T. hemprichii (Ehrenberg) Ascherson are widely distributed in shallow coastal areas in the tropics and subtropics of the Western Atlantic and Indo-Pacific, respectively (den Hartog, 1970; Phillips and Menez, 1988; Spalding et al., 2003), and they are considered to be ‘twin species’. The current hypothesis, based on paleographical data, is that they

Early warning indicators for river nutrient and sediment loads in tropical seagrass beds: A benchmark from a near-pristine archipelago in Indonesia

In remote, tropical areas human influences increase, potentially threatening pristine seagrass systems. We aim (i) to provide a bench-mark for a near-pristine seagrass system in an archipelago in East Kalimantan, by quantifying a large spectrum of abiotic and biotic properties in seagrass meadows and (ii) to identify early warning indicators for river sediment and nutrient loading, by comparing the seagrass meadow properties over a gradient with varying river influence. Abiotic properties of water column, pore water and sediment were less suitable indicators for increased sediment and nutrient loading than seagrass properties. Seagrass meadows strongly responded to higher sediment and nutrient loads and proximity to the coast by decreasing seagrass cover, standing stock, number of seagrass species, changing species composition and shifts in tissue contents. Our study confirms that nutrient loads are more important than water nutrient concentrations. We identify seagrass system variables that are suitable indicators for sediment and nutrient loading, also in rapid survey scenarios with once-only measurements.

Abundance, edge effect, and seasonality of fauna in mixed-species seagrass meadows in southwest Sulawesi, Indonesia

Abstract Motile fauna species in two mixed-species seagrass meadows with different canopy structure were studied on an uninhabited island in the Spermonde Archipelago, Sulawesi, Indonesia. The main focus of the study was to assess the edge effect and seasonal abundance of macrobenthic invertebrates. Fish and infauna densities were determined as well. Fauna was counted using permanent transects (macrobenthic invertebrates), visual census (fish species), and sediment cores (infauna). Both meadows had a comparable distribution of motile fauna species with polychaetes (35% of total abundance), bivalves (27%) and sipunculids (25%) accounting for the largest part of the total faunal abundance. The closed canopy meadow (high seagrass leaf biomass) had an overall higher faunal abundance compared with the open canopy meadow (low seagrass leaf biomass) (1133 vs. 751 individuals m−2). Although infauna abundance was comparable between the meadows, macrobenthic invertebrates (crustaceans, echinoderms, and molluscs) and fishes were more abundant in the closed canopy meadow, with only a few individual species more abundant in the open canopy meadow. The effect of distance from the meadow edge on macrobenthic invertebrate abundance was significant, with higher abundances towards the interior of the seagrass meadows, but for fish abundance no significant differences were found. Effects of seasonality (rainy vs. dry season) on macrobenthic invertebrate abundance were only significant for molluscs. We concluded that macrobenthic invertebrate abundance was most influenced by seagrass canopy structure, followed by meadow edge effects, and least by seasonality. Comparisons of faunal abundance in seagrass meadows need thus to include information on these three variables.

Exposure based waiving in environmental risk assessment: A tiered approach

ABSTRACT The REACH legislation describes the “Exposure Based Waiving” (EBW) methodology, that allows reduction of animal tests and that facilitates the Chemical Safety Assessments. We introduced a tiered EBW decision strategy for the aquatic environment. Tier 0 in this strategy justifies waiving if it can be demonstrated that exposure of organisms to a chemical will be practically zero (i.e., if no environmental emissions during the full life-cycle of a chemical are to be expected. Tier 1 uses tabular data, derived from physical–chemical properties of a chemical and emission data, to identify whether the environmental exposure levels are less than the conservative toxicological reference value “Threshold of Toxicological Concern” (TTC). To this end, systematic exposure calculations have been carried out with a hypothetical chemical dataset, covering the full chemical spectrum for neutral organic substances. In tier 2, PEC and PNEC are to be assessed probabilistically in order to address the probability of effects. Following this strategy, risk can be shown to be sufficiently low, using minimal exposure and hazard data. Our tiered EBW concept is illustrated by a case study for the substance dibutylphthalate with the endpoint of fresh water aquatic risks.