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N M van Straalen

Publications and source records attributed to N M van Straalen.

At least 19 recordsLinked to original sources
PubMed2006

Additive genetic variation of transcriptional regulation: metallothionein expression in the soil insect Orchesella cincta.

Field-selected metal tolerance in Orchesella cincta is correlated with overexpression of the single copy cadmium (Cd) inducible metallothionein (mt). Previously, we have demonstrated large phenotypic variation in mt gene expression, and a higher frequency of high-expression phenotypes in a tolerant population. Here, we describe midparent-offspring regression analysis of mt gene expression in a laboratory culture originating from a noncontaminated natural population. Families were either not exposed (n=47) or exposed to 0.5 micromol Cd per gram dry food (n=46). Mean mt gene expressions normalized to 28S rRNA and beta-actin RNA were generated using real-time RT-PCR applied to parents and offspring RNA and subjected to regression analysis. A significant heritability (h2) for mt gene expression was estimated between 0.36 (beta-actin normalized) and 0.46 (28S normalized) in Cd exposed families. Nontreated families did not yield a significant h2 value. Restriction Fragment Length Polymorphism analysis of the metallothionein promoter sequence revealed eight promoter alleles that show structural variation. Three alleles show increased frequencies in families with high mt expression. Another gene, croquemort (isolated from a differential screening for 1 micromole Cd treatment) showed no h2 of gene expression in response to 0.5 micromol Cd. This gene codes for a receptor-protein involved in recognition of apoptotic cells and may participate in the general stress response. The present data suggest that evolution of metal tolerance in O. cincta can occur in the field by selection for high mt expression due to structural changes in mt cis-regulation.

Adaptation, Physiological↗
PubMed2005

Bioavailability of contaminants estimated from uptake rates into soil invertebrates.

It is often argued that the concentration of a pollutant inside an organism is a good indicator of its bioavailability, however, we show that the rate of uptake, not the concentration itself, is the superior predictor. In a study on zinc accumulation and toxicity to isopods (Porcellio scaber) the dietary EC(50) for the effect on body growth was rather constant and reproducible, while the internal EC(50) varied depending on the accumulation history of the animals. From the data a critical value for zinc accumulation in P. scaber was estimated as 53 microg/g/wk. We review toxicokinetic models applicable to time-series measurements of concentrations in invertebrates. The initial slope of the uptake curve is proposed as an indicator of bioavailability. To apply the dynamic concept of bioavailability in risk assessment, a set of representative organisms should be chosen and standardized protocols developed for exposure assays by which suspect soils can be evaluated.

Animals↗
PubMed2004

Pyrene biotransformation and kinetics in the hepatopancreas of the isopod Porcellio scaber.

Various techniques exist for polycyclic aromatic hydrocarbon (PAH) determination in environmental samples, but an adequate risk assessment of PAHs should include aspects such as bioavailability of the contaminant and biotransformation capacity of the species under investigation. In this study, we provided an analysis of the kinetics of pyrene in the terrestrial isopod Porcellio scaber. Isopods were exposed to pyrene in their food (10 microg/g d/w) for 7 days followed by an elimination period of 7 days. The animals were dissected, and the hepatopancreases were analyzed for pyrene biotransformation products; nonmetabolised pyrene in the gut was also monitored. Concentrations of 1-hydroxypyrene in the hepatopancreas were very low. Almost all of the pyrene was found as three conjugates: pyrene-1-glucoside, pyrene-1-sulfate, and a third unknown 1-hydroxypyrene conjugate. Concentrations of the metabolites were extremely variable between individuals because of variable feeding activity. An apparent steady state was reached already after 24 hours of exposure, whereas elimination was complete 48 hours after ending the exposure. This rapid response to changes in the exposure concentration shows that terrestrial isopods have a high biotransformation capacity for PAHs. The data show that concentrations of parent PAHs will not provide a good indication of exposure in rapidly metabolizing invertebrates such as isopods; instead, pyrene metabolites may be considered a promising biomarker for bioavailability of PAH contamination in the field.

Animals↗
PubMed2001

Two metal-binding peptides from the insect Orchesella cincta (Collembola) as a result of metallothionein cleavage.

Metallothionein (MT) is an ubiquitous heavy metal-binding protein which has been identified in animals, plants, protists, fungi and bacteria. In insects, primary structures of MTs are known only for Drosophila and the collembolan, Orchesella cincta. The MT cDNA from O. cincta encodes a 77 amino acid protein with 19 cysteines. Isolations of the protein itself have demonstrated the presence of two smaller metal-binding peptides, whose amino acid sequences correspond to parts of the cDNA, and which apparently result from cleavage of the native protein. The present study was undertaken to complete the picture of cleavage sites within the MT protein by applying protein isolation techniques in combination with mass spectrometry and N-terminal sequence analysis. Further, recombinant expression allowed us to study the intrinsic stability of the MT and to perform in vitro cleavage studies. The results show that the MT from O. cincta is specifically cleaved at two sites, both after the amino acid sequence Thr-Gln (TQ). One of these sites is located in the N-terminal region and the other in the linker region between two putative metal-binding clusters. When expressed in Escherichia coli, the recombinant O. cincta MT can be isolated in an uncleaved form; however, this protein can be cleaved in vitro by the proteolytic activity of O. cincta. In combination with other studies, the results suggest that the length of the linker region is important for the stability of MT as a two domain metal-binding protein.

Amino Acid Sequence↗
PubMed2001

A review of the effects of multiple stressors on aquatic organisms and analysis of uncertainty factors for use in risk assessment.

Risk assessment procedures use toxicity tests in which organisms are subjected to chemicals under otherwise constant and favorable experimental conditions. Because variable and suboptimal environmental conditions are common aspects of natural ecosystems, the hazard of underestimation of risk arises. Therefore, an uncertainty factor is used in the extrapolation of results of standard toxicity tests to field situations. The choice for these uncertainty factors is based on little ecological evidence. This review discusses studies on the toxicity of various chemicals to aquatic organisms, modified by temperature, nutritional state and salinity, excluding papers on changes in bioavailability of compounds. Collected data were analyzed quantitatively to evaluate the validity of toxicity data obtained from standard toxicity tests in the laboratory under field conditions. Generally, organisms living under conditions close to their environmental tolerance limits appeared to be more vulnerable to additional chemical stress. Usually, increasing temperature and decreasing food or nutrient level raised toxicity. The influence of salinity was less clear; metal toxicity increased with decreasing salinity, toxicity of organophosphate insecticides increased with higher salinity, while for other chemicals no clear relationship between toxicity and salinity was observed. The interactions can be explained by several physical and physiological processes, acting on factors such as bioavailability, toxicokinetics, and sensitivity of organisms. Quantitative analysis of data indicated that an uncertainty factor for the laboratory to field extrapolation should be smaller than one for an ecosystem in a temperate region, while a factor greater than one would be appropriate for systems nearby discharge points of cooling water. The factor should be greater than one when varying nutritional state is concerned, but smaller than one with respect to salinity. Dependent on the effect parameter used, the differences in toxicity between laboratory and relevant field situations ranged from a factor of 2.6 to 130 and 1.7 to 15 for the two temperature conditions and 1.2 to 10 for nutritional state. A salinity increase from freshwater to marine water decreased toxicity by a factor of 2.1. However, as less extreme salinity changes are more relevant under field conditions, the change in toxicity is probably much smaller. To obtain uncertainty factors that sufficiently protect natural systems without being overprotective, additional research is required.

Animal Nutritional Physiological Phenomena↗
PubMed2001

Characterization of enzymes involved in biotransformation of polycyclic aromatic hydrocarbons in terrestrial isopods.

Little is known about the capacity of terrestrial invertebrates to transform organic soil pollutants such as polycyclic aromatic hydrocarbons (PAHs). Studies were designed to characterize microsomal mixed function oxygenase and accompanying conjugation enzymes from the hepatopancreas of the terrestrial isopods Porcellio scaber and Oniscus asellus using pyrene and 1-hydroxypyrene as model substrates. The hydroxylation of pyrene and the formation of pyreneglucoside and pyrenesulfate appeared to be sensitive measures for the activity of cytochrome P450 aryl hydrocarbon hydroxylase (AHH), uridinediphosphateglucosyltransferase (UDPGT), and aryl sulfotransferase (ST), respectively. Treatment with the antibiotic riphampicine demonstrated that the enzyme activities originate from the animals themselves and not from symbiotic microflora present in the hepatopancreas and the gut. In both species, ST has a very high affinity for 1-hydroxypyrene with Km values two orders of magnitude lower than that of UDPGT. The Vmax values of UDPGT, however, are 10- to 20-fold higher than that of ST. Taking the P450 activities into consideration, both species are expected to transform PAHs in an equally effective way. When the isopods were fed with food containing benz[a]pyrene and 3-methyl-cholanthrene, none of the enzyme activities appeared to be inducible except for a small enhancement of UDPGT in O. asellus. Our findings indicate that terrestrial isopods have a high, noninducible capacity for biotransformation of PAHs and that the sulfate conjugation pathway is as important as the carbohydrate conjugation pathway. This conclusion is consistent with the low body residues of parent PAHs found in the field.

Animals↗
PubMed2000

TE-AFLP: combining rapidity and robustness in DNA fingerprinting.

A new type of fingerprinting technique is presented, based on amplified fragment length polymorphism (AFLP). Rather than two endonucleases as in AFLP, we propose the use of three enzymes, hence the method is called three endonuclease (TE)-AFLP. Genomic DNA is digested and two sets of adapters are selectively ligated onto the restriction fragments in a single reaction volume. No adapters complementary to the ends generated by a frequent cutter are added. Due to the addition of a third endonuclease, the TE-AFLP method provides a high discriminatory power and a reduction in the number of bands. The latter makes it especially suitable for the analysis of complex genomes. TE-AFLP fingerprints are suitable for detection by automatic fluorescent sequencers and are obtained in less than half the time and at reduced costs compared to a typical AFLP. The reliability of this method was investigated by determining the influence of varying digestion, ligation and PCR components on the fingerprint. Moreover, cross-experiments to study inheritance of loci were performed with a primitive insect and with tomato strains. The features of TE-AFLP are discussed in comparison with conventional AFLP.

Animals↗
PubMed2000

Metallothionein-bound cadmium in the gut of the insect Orchesella cincta (Collembola) in relation to dietary cadmium exposure.

Metallothionein is considered to be a potential biomarker for heavy metal exposure in the terrestrial environment. However, limited information is available on metallothioneins from insects, a major class of terrestrial invertebrates. In this study we have quantified metallothioneins in the springtail Orchesella cincta by determining metallothionein-bound cadmium after separation of these proteins using gel filtration and reversed phase chromatography from total body homogenates of animals dietary exposed to different concentrations of cadmium. Furthermore, we have studied in more detail where cadmium and metallothionein-bound cadmium is located within this animal. The concentration of metallothionein-bound cadmium increases with the exposure concentration in the same way as the total internal concentration. Both reach a plateau at an exposure concentration of approximately 1.0 micromol Cd/dry food. Cadmium is primarily located within the gut of O. cincta and isolation of metallothionein from this organ gives results identical to isolations from total bodies. Based on this results an estimation of the metallothionein level at the highest exposure concentration results in a concentration of about 115 microg metallothionein/g fresh gut. The O. cincta metallothionein gives the possibility of using this protein as a biomarker for heavy metal exposure in soil insects.

Animals↗
PubMed1999

Combining life-history and toxicokinetic parameters to interpret differences in sensitivity to cadmium between populations of Polycelis tenuis (Platyhelminthes).

Five populations of the planarian Polycelis tenuis, collected from four locations in a metal contaminated stream and from one location in an unpolluted tributary stream, were compared for their sensitivity to cadmium by measuring survival, reproduction, and body size changes during 28 days of exposure via the water. Survival data and bioconcentration of cadmium measured at the end of the experiment enabled the use of a kinetic-based toxicity model, estimating the lethal body concentration, the uptake rate constant, the elimination rate constant, and the ultimate LC(50) as estimated toxicokinetic parameters. Accurate body size selection and a one-month acclimatization period to standardized laboratory conditions were applied to enhance the comparability between populations. An increased elimination rate constant and a greater ultimate LC(50) were estimated for one of the populations, located downstream from an ancient lead-zinc mine. The cadmium concentration causing an effect on reproduction varied considerably (a factor of 10) among populations but did not differ significantly between populations. For the number of reproducing individuals as a function of cadmium concentration, EC(50) and steepness of slope of the concentration/effect relationship tended to be correlated positively (P<0.10), indicating that selection in the field may have occurred. Cadmium was found to enhance shrinkage of P. tenuis under conditions of food limitation.

Animals↗
PubMed1996

Uptake and elimination of benzo[a]pyrene in the terrestrial isopod Porcellio scaber.

In isopods from contaminated sites relatively low levels of high molecular weight polycyclic aromatic hydrocarbons (PAHs) have been observed, which may be caused by either a low bioavailability or a high elimination rate. To shed light on this, the uptake and elimination rates of benzo[a]pyrene were estimated for the isopod Porcellio scaber. The isopod was fed contaminated food (100 microg benzo[a]pyrene/g dwt) for seven weeks followed by four weeks of untreated food. The hindguts of the animals were removed prior to analysis to exclude food material from the body. Benzo[a]pyrene concentrations were log-normally distributed among the individuals. The high inter-individual variation in benzo[a]pyrene content could not be explained from differences in sex, the estimated amount of food in the hindgut, or the body weight. A one-compartment model fitted to the isopod concentrations estimated an assimilation rate of 2.9 microg benzo[a]pyrene/g dwt day, an elimination rate constant of 1.1/day and an equilibrium concentration of 2.5 microg benzo[a]pyrene/g dwt. According to the model 68% of the isopod population had an equilibrium concentration between 1.0 and 7.2 microg benzo[a]pyrene/g dwt day with a benzo[a]pyrene half-life ranging between 0.4 and 1.3 days. The assimilation efficiency was estimated at 20 to 40% of the ingested benzo[a]pyrene. The tissue distribution of benzo[a]pyrene was investigated in a separate experiment. Trace levels of benzo[a]pyrene were detected in haemolymph samples, demonstrating absorption and transport of the compound in the isopod. It is concluded that dietary benzo[a]pyrene is available for uptake to the isopod and that low residues of the compound observed in field isopods are the result of a high elimination rate rather than a reduced bioavailability. As PAHs from soil appear to be available to soil invertebrates, the widespread contamination of the soil from atmospheric emissions is of some concern, especially since the observed elimination may be linked to metabolic activation of PAHs.

Animals↗
PubMed1996

Trace metals in populations of freshwater isopods: influence of biotic and abiotic variables.

Trace metal levels in water, sediments and freshwater isopods from 28 different water systems in the Netherlands were measured during the period of 1986 to 1989. Distinct element-specific internal distribution patterns were present, with Cd and Cu stored mainly in the hepatopancreas (30-60% of total body burden) and Pb and Zn in the hindgut and exoskeleton with hemolymph. Mean whole-body concentrations of the non-essential elements Cd and Pb in individually analyzed isopods varied over three orders of magnitude between populations. The variability of Zn and Cn were within one order of magnitude difference. The variability of trace metal levels between populations exceeded within-population variability. Within-population variability was related to seasonal and biological factors such as body weight, sex, reproductive state, and species abundance. The highest concentrations were found in small juvenile animals compared to adults, females compared to males, and Proasellus meridianus compared to Asellus aquaticus. However, after correction for size effects using a power-curve regression model no significant differences remained between sex and species. Seasonal fluctuations accounted for 33-79% of the within population variability. Trace metal levels in isopods were predicted from concentrations in water and sediments in combination with aqueous Ca, Cl-, DOC, and sediment characteristics (Org-C, clay, CaCO3) using a multiple regression model. With this predictive model 42-63% of the variance could be explained. In situ determined partitioning coefficients (apparent BCF, biota-sediment BSAF, and sediment-water distribution coefficient Kd) varied between locations and covaried with factors related to trace metal bioavailability (aqueous Ca, Cl- and DOC, sediment Org-C, clay, and CaCO3). Especially for Cd and Cu field-derived BCF values were in agreement with previously reported experimental studies. It is concluded, that A. aquaticus may be a suitable candidate-organism for biomonitoring available trace metal levels in littoral freshwater systems. Finally, some practical recommendations are given for future field surveys with freshwater isopods with respect to sample size, allometric standardization, period of sampling and statistical design.

Analysis of Variance↗
PubMed1993

Chronic ecotoxicity of mixtures of Cu, Zn, and Cd to the zebra mussel Dreissena polymorpha.

Organisms in contaminated freshwater ecosystems are often exposed to a variety of toxicants for their entire lifetime. To evaluate the ecological consequences of these long-term contaminations, the effects of mixtures of heavy metals on the filtration rate and survival of the freshwater mussel Dreissena polymorpha were studied during chronic exposure. In laboratory experiments, mussels were exposed to equitoxic mixtures of Cu + Zn, Cu + Cd, Zn + Cd, and Cu + Zn + Cd in concentrations causing a 50% decrease in filtration rate in short-term (48 hr) experiments. The filtration rate was measured once a week, during a 9- to 10-week exposure period. For all metal combinations effects on mortality increased when exposure time was prolonged from 48 hr to 9-10 weeks. In contrast, the effects on filtration rate did not increase, indicating that the filtration rate was related to the metal mixture concentration in the water, but not related to the metal concentrations in the mussels. Consequently, the effects on mortality and filtration rate were not related. In short-term experiments Cu + Cd were more than concentrations additive, whereas in chronic experiments Cu + Cd were strongly less than additive, indicating a loss of potential for additivity during prolonged exposure. In general, Cu, Zn, and Cd did not affect each others uptake. It was concluded that the chronic effects of mixtures could not be predicted from their short-term effects nor from the chronic effects of the metals tested individually.

Animals↗
PubMed1989

Ecotoxicological evaluation of soil quality criteria.

To implement the Soil Protection Act of 1986, the Dutch Ministry of Housing, Physical Planning, and Environment has recently proposed a list of soil quality reference values. These values are, as yet, insufficiently based on ecotoxicological evidence. In this paper, a three-step procedure of risk assessment for soil contaminants is proposed. Arguing from experimental results concerning no observed effect concentrations for a set of selected soil organisms, the method aims at protecting a certain fraction of soil life, taking factors such as soil organic matter and clay content into account. When applied to cadmium, a concentration protecting 95% of soil invertebrates is estimated as 0.16 micrograms/g for a standard soil. The value of 0.8 micrograms/g, as proposed by the Dutch authorities, may, given the present variation and uncertainty of toxicity data, protect about 85% of the soil invertebrate fauna. It is concluded that even low levels of cadmium in soil may endanger the functioning of some sensitive soil animal species.

Animals↗
PubMed1989

Population consequences of cadmium toxicity in soil microarthropods.

Chronic toxicity experiments were performed using the collembolan Orchesella cincta (L.) and the oribatid mite Platynothrus peltifer (Koch), which were exposed to various levels of cadmium in the food (green algae). Experimental results were combined with life-history information to obtain realistic estimates of the intrinsic rate of population increase and its sensitivity to Cd stress. Chronic LC50 values for dietary exposure to Cd were estimated as 1.60 mumol/g for O. cincta and 3.18 mumol/g for P. peltifer. No-observed-effect concentrations (NOECs) for growth and reproduction were 0.042 mumol/g for O. cincta and 0.026 mumol/g for P. peltifer. The main effects of Cd were, however, different in each species. In O. cincta, Cd affected primarily female growth, without a direct effect on reproduction; in P. peltifer, the effect was primarily on reproduction. Uptake of Cd was higher in P. peltifer than in O. cincta, and caused a loss of zinc in the former species. As a consequence of their differing physiological responses to Cd, mites and collembolans also reacted differently in their population growth rates. The capacity for population increase of mites appeared to be rather sensitive to Cd, while collembolans were able, to some extent, to maintain their capacity for increase, in spite of toxic effects at the individual level. These results may contribute to developing ecotoxicological theory for the population consequences of toxic action in species with diverging life histories. Soil microarthropods may be suitable test organisms for evaluating the risk of chemicals to the soil ecosystem.

Animals↗
PubMed1989

Bioaccumulation of cadmium by the freshwater isopod Asellus aquaticus (L.) from aqueous and dietary sources.

Experiments were conducted to determine the kinetics and relative importance of aqueous and dietary uptake of cadmium by the freshwater isopod Asellus aquaticus (L.). Test animals were exposed during 30 days to aqueous Cd in a continuous flow system (exposure levels: 0.2 - 10 microg litre(-1)) and kept on a diet of previously contaminated Elodea sp. (range of Cd concentrations: 2-350 microg g(-1), dry weight). Preceding semi-static experiments on dosage-control of the dietary factor revealed a rapid uptake of Cd by Elodea, with relatively high concentration factors (CF), which ranged from 4.8 to 5.5 (dry weight log (CF) after 16 days). For Asellus uptake from water appeared to be the predominant route. Highly significant bioconcentration of cadmium from water was observed in the animals, even at exposure levels below 1.0 microg litre(-1). In the various treatments, direct uptake from water accounted for 50-98% of the body burdens after 30 days exposure. The experimental results were described with a first order one-compartment bioaccumulation model. Model parameter estimates (mean +/- standard error) were obtained for rate constant of uptake (560 +/- 110 day(-1)), rate constant of elimination (0.032 +/- 0.017 day(-1)) and assimilation efficiency of Cd uptake from food (1.1 +/- 0.7%). The (dry weight) bioconcentration factor (BCF) and bioaccumulation factor (BAF) for extrapolated steady state conditions were estimated at 18 000 (BCF) and 0.08 (BAF). Experiments conducted at two different pH levels (5.9 versus 7.6) revealed no significant effects of pH on the uptake of aqueous Cd by the isopods. The results are discussed in relation to their potential significance to the field situation.

Journal Article↗
PubMed1986

Histochemical staining of cadmium thiolate clusters in livers of rats treated chronically with cadmium.

In livers of rats exposed to varying doses of CdCl2 80-90% of the cadmium content present in the fresh tissue is retained if these livers are fixed with a neutral or acid formalin fixative. Cadmium assays during different stages of the staining procedure for protein bound disulphides show the ability of this staining to demonstrate cadmium thiolate clusters next to disulphides. The methods described may also be useful in gaining more insight in the mechanism involved in fixation and staining procedure of some other metals.

Animals↗