Radiotherapy induces an increase in serum antioxidant capacity reflecting tumor response.

Background and purpose: Radiotherapy (RT) is a mainstay component of treatment for patients with head and neck squamous cell carcinoma (HNSCC), but responses vary. As RT relies upon oxidative damage, antioxidant expression in response to RT-induced reactive oxygen species (ROS) could compromise treatment response. We aimed to examine local and systemic antioxidant responses to increased RT-induced ROS in relation to treatment success. Materials and methods: Nuclear factor erythroid 2-related factor 2 (NRF2), the main antioxidant transcription factor, was immunofluorescently stained in FaDu cells and in tumor biopsies of patients with oral cavity/oropharynx HNSCC before and after five fractions of RT. Besides, total antioxidant capacity (TAC) was analyzed in HNSCC tumor cells in vitro and in serum of HNSCC patients before, during, and after RT. Results: Data revealed an increase in NRF2 expression and TAC in head and neck cancer cells in vitro over the course of 5 daily fractions of 2 Gy. In accordance, also in patients' tumors NRF2 expression increased, which was associated with increased serum TAC during RT. Increasing serum TAC was related to impaired local tumor control. Conclusion: Radiation induced NRF2 expression and upregulated TAC, which may compromise the effect of RT-induced ROS. Changes in serum TAC during RT could serve as a novel predictor of treatment outcome in HNSCC patients.Medical Ethics Review Committee (CMO) approval - CMO number: 2007/104.

Changes to insulin sensitivity in glucose clearance systems and redox following dietary supplementation with a novel cysteine-rich protein: A pilot randomized controlled trial in humans with type-2 diabetes.

We recently developed a novel keratin-derived protein (KDP) rich in cysteine, glycine, and arginine, with the potential to alter tissue redox status and insulin sensitivity. The KDP was tested in 35 human adults with type-2 diabetes mellitus (T2DM) in a 14-wk randomised controlled pilot trial comprising three 2×20 g supplemental protein/day arms: KDP-whey (KDPWHE), whey (WHEY), non-protein isocaloric control (CON), with standardised exercise. Outcomes were measured morning fasted and following insulin-stimulation (80 mU/m2/min hyperinsulinaemic-isoglycaemic clamp). With KDPWHE supplementation there was good and very-good evidence for moderate-sized increases in insulin-stimulated glucose clearance rate (GCR; 26%; 90% confidence limits, CL 2%, 49%) and skeletal-muscle microvascular blood flow (46%; 16%, 83%), respectively, and good evidence for increased insulin-stimulated sarcoplasmic GLUT4 translocation (18%; 0%, 39%) vs CON. In contrast, WHEY did not effect GCR (-2%; -25%, 21%) and attenuated HbA1c lowering (14%; 5%, 24%) vs CON. KDPWHE effects on basal glutathione in erythrocytes and skeletal muscle were unclear, but in muscle there was very-good evidence for large increases in oxidised peroxiredoxin isoform 2 (oxiPRX2) (19%; 2.2%, 35%) and good evidence for lower GPx1 concentrations (-40%; -4.3%, -63%) vs CON; insulin stimulation, however, attenuated the basal oxiPRX2 response (4%; -16%, 24%), and increased GPx1 (39%; -5%, 101%) and SOD1 (26%; -3%, 60%) protein expression. Effects of KDPWHE on oxiPRX3 and NRF2 content, phosphorylation of capillary eNOS and insulin-signalling proteins upstream of GLUT4 translocation AktSer437 and AS160Thr642 were inconclusive, but there was good evidence for increased IRSSer312 (41%; 3%, 95%), insulin-stimulated NFκB-DNA binding (46%; 3.4%, 105%), and basal PAK-1Thr423/2Thr402 phosphorylation (143%; 66%, 257%) vs WHEY. Our findings provide good evidence to suggest that dietary supplementation with a novel edible keratin protein in humans with T2DM may increase glucose clearance and modify skeletal-muscle tissue redox and insulin sensitivity within systems involving peroxiredoxins, antioxidant expression, and glucose uptake.

Tamoxifen induces radioresistance through NRF2-mediated metabolic reprogramming in breast cancer.

BACKGROUND: Recently, we reported that tamoxifen-resistant (TAM-R) breast cancer cells are cross-resistant to irradiation. Here, we investigated the mechanisms associated with tamoxifen-induced radioresistance, aiming to prevent or reverse resistance and improve breast cancer treatment. METHODS: Wild-type ERα-positive MCF7 and ERα-negative MDA-MB-231 breast cancer cells and their TAM-R counterparts were analyzed for cellular metabolism using the Seahorse metabolic analyzer. Real-time ROS production, toxicity, and antioxidant capacity in response to H2O2, tamoxifen, and irradiation were determined. Tumor material from 28 breast cancer patients before and after short-term presurgical tamoxifen (ClinicalTrials.gov Identifier: NCT00738777, August 19, 2008) and cellular material was analyzed for NRF2 gene expression and immunohistochemistry. Re-sensitization of TAM-R cells to irradiation was established using pharmacological inhibition. RESULTS: TAM-R cells exhibited decreased oxygen consumption and increased glycolysis, suggesting mitochondrial dysfunction. However, this did not explain radioresistance, as cells without mitochondria (Rho-0) were actually more radiosensitive. Real-time measurement of ROS after tamoxifen and H2O2 exposure indicated lower ROS levels and toxicity in TAM-R cells. Consistently, higher antioxidant levels were found in TAM-R cells, providing protection from irradiation-induced ROS. NRF2, a main activator of the antioxidant response, was increased in TAM-R cells and in tumor tissue of patients treated with short-term presurgical tamoxifen. NRF2 inhibition re-sensitized TAM-R cells to irradiation. CONCLUSION: Mechanisms underlying tamoxifen-induced radioresistance are linked to cellular adaptations to persistently increased ROS levels, leading to cells with chronically upregulated antioxidant capacity and glycolysis. Pharmacological inhibition of antioxidant responses re-sensitizes breast cancer cells to irradiation.

A comparative study of colour and perfusion between two different post surgical scars. Do the laser Doppler imager and the colorimeter measure the same features of a scar?

BACKGROUND/PURPOSE: The purpose of this study was to investigate the influence of different located post surgical scars on both perfusion and redness. The pattern of change and correlation between perfusion and redness of post surgical scars is also examined. METHODS: In this study, we measured redness and perfusion of the abdominal and breast scar of 24 women undergoing breast reconstruction with Deep Inferior Epigastric Perforator Free Flap surgery with the Minolta Chromameter CR-400/410 and the Moor Instruments laser Doppler imager 12IR, respectively, at different intervals post-operatively. RESULTS: The laser Doppler imager gives significantly higher values for the abdominal compared with the breast scar. There was no consistent correlation found between perfusion and redness at the different test moments for both locations. The scores of both parameters were significantly associated after 9 months follow-up for both locations. CONCLUSION: Scars closed with higher mechanical force show higher perfusion and prolonged activity; and more redness is associated with more perfusion for both post surgical scars. Nevertheless, there was no consistent correlation found between these parameters making the laser Doppler imager and the Colorimeter still non-replaceable instruments.

Assessment of Blood Hemodynamics by USPIO-Induced R(1) Changes in MRI of Murine Colon Carcinoma.

The objective of this study is to assess whether ultrasmall superparamagnetic iron oxide (USPIO)-induced changes of the water proton longitudinal relaxation rate (R(1)) provide a means to assess blood hemodynamics of tumors. Two types of murine colon tumors (C26a and C38) were investigated prior to and following administration of USPIO blood-pool contrast agent with fast R(1) measurements. In a subpopulation of mice, R(1) was measured following administration of hydralazine, a well-known blood hemodynamic modifier. USPIO-induced R(1) increase in C38 tumors (DeltaR(1) = 0.072 +/- 0.0081 s(-1)) was significantly larger than in C26a tumors (DeltaR(1) = 0.032 +/- 0.0018 s(-1), N = 9, t test, P < 0.001). This was in agreement with the immunohistochemical data that showed higher values of relative vascular area (RVA) in C38 tumors than in C26a tumors (RVA = 0.059 +/- 0.015 vs. 0.020 +/- 0.011; P < 0.05). Following administration of hydralazine, a decrease in R(1) value was observed. This was consistent with the vasoconstriction induced by the steal effect mechanism. In conclusion, R(1) changes induced by USPIO are sensitive to tumor vascular morphology and to blood hemodynamics. Thus, R(1) measurements following USPIO administration can give novel insight into the effects of blood hemodynamic modifiers, non-invasively and with a high temporal resolution.

Observation of two-photon speckle patterns.

We report the observation of speckle patterns in quantum correlations within light that is scattered by a disordered medium. The random medium is illuminated with spatially entangled photon pairs, and fourth-order speckle patterns are spatially resolved by two independently scanning detectors. Spatial entanglement gives two-photon speckle a much richer structure than ordinary one-photon speckle. Our experiments demonstrate that two-photon speckle from a surface scatterer and a volume scatterer look entirely different.

Carotid atherosclerotic plaques stabilize after stroke: insights into the natural process of atherosclerotic plaque stabilization.

OBJECTIVE: Rupture of unstable atherosclerotic plaques is the pathological substrate for acute ischemic events. Underlying cellular and molecular characteristics of plaque rupture have been studied extensively. However, the natural course of symptomatic plaque remodeling after ischemic events is relatively unexplored. METHODS AND RESULTS: Atherosclerotic carotid plaques were obtained from 804 symptomatic (stroke=204 and TIA=426) and asymptomatic (n=174) patients undergoing carotid endarterectomy. The presence of macrophages, smooth muscle cells (SMC), collagen, calcification, and lipid-core size were assessed histologically. At protein level, inflammatory mediators (interleukin [IL]-2, IL-4, IL-5, IL-8, IL-10, IL-12p70, interferon-gamma [INF-gamma], tumor necrosis factor-alpha [TNF-alpha], matrix degrading proteinases (MMPs), and an apoptosis marker (caspase-3) were determined. We associated plaque characteristics with time elapsed between the latest event and surgery. Early after stroke and TIA, plaques revealed an unstable phenotype. After stroke, the content of macrophages decreased significantly with time (P=0.02), whereas SMC content tended to increase. At protein level, IL-6, IL-8 expression levels and caspase activity strongly decreased after stroke or TIA. CONCLUSIONS: Symptomatic carotid lesions remodel into more stable plaques over time after stroke. Changes in IL-6 and IL-8 and caspase preceded the decrease of macrophages. These temporal phenotypic plaque alterations should be taken into account for biomarker and therapeutic target validation studies using human atherosclerotic plaques.

Free myocutaneous latissimus dorsi flap transfer in total knee arthroplasty.

The purpose of this article is to present our experience with free myocutaneous latissimus dorsi flap transfer in total knee arthroplasty in case of insufficient soft tissue prior to operation ('prophylactic indication'). Fourteen patients who underwent simultaneous flap surgery in the context of total knee arthroplasty because of insufficient soft tissue are reviewed in a retrospective clinical study. The following criteria were examined: (1) aetiology of the soft-tissue defect, (2) number of previous operations, (3) status of the knee extensor mechanism classified as complete, partial or missing, (4) primary wound healing, (5) complications and (6) active range of motion (ROM). Insufficient soft tissue resulted from multiple previous operations in 10 patients and large post-traumatic defects in four patients. All patients had 5-23 (mean 10.2) previous operations before free latissimus dorsi transfer. The status of the extensor mechanism was complete in one, partial in nine and missing in four patients. Primary wound healing could be achieved in eight patients. After free latissimus dorsi transfer, skin breakdown at the recipient site occurred in five patients. Secondary skin grafting was carried out in four patients and a fasciocutaneous flap in one patient. There were three late recurrences of infection, with ultimate removal of the knee prosthesis and conversion to arthrodesis. Average active ROM prior to surgery was for extension/flexion 0-9-28 degrees . One year after surgery the average active ROM was 0-6-75 degrees . A free myocutaneous latissimus dorsi flap transfer is rarely indicated in total knee arthroplasty and should only be considered for defects which cannot be covered by a pedicled (medial gastrocnemius) flap. Free latissimus dorsi transfer makes prosthesis implantation possible, prevents postoperative knee stiffness because of soft tissue and/or scar constriction and shows a low rate of severe complications in patients with a high risk of wound-healing problems. Moreover, transfer of well-vascularised tissue will improve trophicity in the knee region, and thus make future operations in this region easier.

Optical characterization of periodically-poled KTiOPO4.

We demonstrate how the Maker fringes that are observable in spontaneous parametric down-conversion (SPDC) give a direct visualization of the poling quality of a periodically-poled crystal. Identical Maker fringes are observed in the optical spectrum of collinear SPDC and the temperature dependence of second harmonic generation. We analyze these Maker fringes via a unified treatment of the tuning curve in crystals with small and slowly-varying deformations of the poling structure. Our theoretical model, based on a Fourier analysis of the poling deformations, distinguishes between duty-cycle variations and variations of the poling phase. The analysis indicates that the poling phase is approximately fixed, while the duty-cycle typically varies between 36% and 64%.

Characterization of late radiation effects in the rat thoracolumbar spinal cord by MR imaging using USPIO.

The aim of this study was to detect late radiation effects in the rat spinal cord using MR imaging with ultra-small particles of iron oxide (USPIO) contrast agent to better understand the development of late radiation damage with emphasis on the period preceding neurological signs. Additionally, the role of an inflammatory reaction was assessed by measuring macrophages that internalized USPIO. T2-weighted spin echo MR measurements were performed at 7T in six rats before paresis was expected (130-150 days post-irradiation, early group), and in six paretic rats (150-190 days post-irradiation, late group). Measurements were performed before, directly after and, only in the early group, 40 h after USPIO administration and compared with histology. In the early group, MR images showed focal regions in grey matter (GM) and white matter (WM) with signal intensity reduction after USPIO injection. Larger lesions with contrast enhancement were located in and around edematous GM of three animals of the early group and five of the late group. Forty hours after injection, additional lesions in WM, GM and nerve roots appeared in animals with GM edema. In the late paretic group, MR imaging showed WM necrosis adjacent to areas with large contrast enhancement. In conclusion, detection of early focal lesions was improved by contrast administration. In the animals with extended radiation damage, large hypo-intense regions appeared due to USPIO, which might be attributed to blood spinal cord barrier breakdown, but the involvement of blood-derived iron-loaded macrophages could not be excluded.

Peri-implant health around screw-shaped c.p. titanium machined implants in partially edentulous patients with or without ongoing periodontitis.

The relationship between periodontitis and peri-implantitis remains a matter of debate. The present study compared, "within" randomly chosen partially edentulous patients (n=84 subjects, 97 jaws), the marginal bone loss around teeth and implants during 5 years (range 3 to 11 years) following the first year of bone remodelling. The patients had all been rehabilitated by means of screw-shape c.p. titanium implants with a machined surface (Brånemark system). During the 5 years observation interval, periodontal parameters (marginal bone and attachment loss, the latter for teeth only) were collected together with data on confounding factors (smoking, oral hygiene, tooth loss). Marginal bone loss was measured through long-cone intra-oral radiographs. The mean "interval" bone loss was significantly (P=0.0001) higher around teeth (0.48+/-0.95 mm) than around implants (0.09+/-0.28 mm). The corresponding data for the "worst" performing tooth (0.99+/-1.25 mm) and implant (0.19+/-0.32 mm) per subject showed the same tendency. Neither attachment nor bone loss around teeth correlated with marginal bone loss around implants. This study indicated that the rate of bone loss around screw-shape c.p. titanium implants with a machined surface (Brånemark system implants) was not influenced by the progression rate of periodontal destruction around the remaining teeth within the same jaw.

Effect of different chlorhexidine formulations in mouthrinses on de novo plaque formation.

BACKGROUND: Chlorhexidine (CHX) 0.2% solution, still the golden standard as mouthrinse for the prevention of plaque formation and development of gingivitis, has some limited side-effects such as extrinsic tooth staining, poor taste, taste disturbance, sensitivity changes in tongue, pain, and the content of alcohol. These side effects led to the search of new formulations. METHODS: In this double-blind, randomised, cross-over study, 16 young dental students with a healthy periodontium, abolished all means of mechanical plaque control during 4 experimental periods of 11 days (separated from each other by a washout period of 3 weeks). During each experimental period, they rinsed 2x daily with one of the following mouthrinses in a randomised order: CHX 0.2% + alcohol (Corsodyl), CHX 0.12% + alcohol (Perio.Aid), CHX 0.12% + sodium fluoride 0.05% (Cariax Gingival) and CHX 0.12% + CPC 0.05% (Perio.Aid, new formulation). After 7 and 11 days of undisturbed plaque formation, clinical parameters were recorded, questionnaires completed and plaque samples (supragingivally and saliva) collected. RESULTS: The CHX 0.12% + alcohol and the CHX 0.12% + CPC 0.05% formulations were as efficient as the CHX 0.2% mouthrinse in retarding de novo plaque formation (proven by clinical observations as well as by anaerobic and aerobic culture data), and always superior (p<0.001) to the CHX 0.12% + sodium fluoride 0.05% solution. The subjective ratings were in favour of the new CHX formulation when compared with the other CHX formulations, especially for taste (p<0.05). CONCLUSIONS: The results of this study demonstrated the potential of a new CHX 0.12% + CPC 0.05% non-alcoholic formulation as an effective anti-plaque and anti-inflammatory agent with reduced unpleasant subjective side-effects.

Effect of different mouthrinses on morning breath.

BACKGROUND: Morning breath odor is an often-encountered complaint. This double-blind, crossover, randomized study aimed to examine the bad breath-inhibiting effect of 3 commercially available mouthrinses on morning halitosis during an experimental period of 12 days without mechanical plaque control. METHODS: Twelve medical students with a healthy periodontium refrained from all means of mechanical plaque control during 3 experimental periods of 12 days (with intervening washout periods of at least 3 weeks). A professional oral cleaning preceded each period. During each experimental period, as the only oral hygiene measure allowed, the students rinsed twice a day with one of the following formulations in a randomized order: CHX-Alc (a 0.2% chlorhexidine [CHX] solution); CHX-NaF (CHX 0.12% plus sodium fluoride 0.05%); or CHX-CPC-Zn (CHX 0.05% plus cetylpyridinium chloride 0.05% plus zinc lactate 0.14%). After 12 days, morning breath was scored via volatile sulfur compound (VSC) level measurements of the mouth air and organoleptic ratings of the mouth air, the expired air, and a scraping of the tongue coating. At the 12-day visit, a questionnaire (subjective ratings) was completed and samples taken from both the tongue coating and the saliva for anaerobic and aerobic culturing and vitality staining. The de novo supragingival plaque formation was also recorded. All parameters were correlated with the baseline registrations. RESULTS: Although oral hygiene during the 3 experimental periods was limited to oral rinses, bad breath parameters systematically improved, with the exception of a slight increase in VSC levels while using CHX-Alc, a finding which was associated with the direct influence of the CHX on the sulfide monitor. The oral microbial load after the use of CHX-NaF remained unchanged, while for the CHX-Alc and CHX-CPC-Zn, significant reductions in both aerobic and anaerobic colony forming units (CFU)/ml were noticed in comparison with baseline data for both tongue coating and saliva samples. The composition of microflora, on the other hand, did not reveal significant changes. The supragingival plaque formation was inhibited, in descending order, by CHX-Alc, CHX-CPC-Zn, and CHX-NaF. The subjective scores for the rinses indicated a higher appreciation for CHX-CPC-Alc and CHX-NaF because of a better taste and fewer side effects. CONCLUSIONS: The results of this study demonstrate that morning halitosis can be successfully reduced via daily use of mouthrinses. CHX-Alc and CHX-CPC-Zn mouthrinses result in a significant reduction of the microbial load of tongue and saliva.

Candida bituminiphila, a novel anamorphic species of yeast.

A novel anamorphic species of yeast belonging to the genus Candida was isolated from tar in Canada. Morphological and physiological observations, as well as phylogenetic analyses, were performed. Conidiophores were produced, were usually short and had sympodial growth, numerous bud scars and a rachis-like structure. They bore one or more conidia. Pseudomycelium was scarcely produced and true mycelium was sparse. No sexual reproduction was observed on corn meal, malt, Gorodkowa, Dextrose Yeast Peptone or V8 agars. Zygoascus hellenicus was physiologically the most closely related species, but it differed from the novel species by its ability to assimilate D-galacturonate and L-rhamnose, ferment sucrose and grow at 37 degrees C. From sequence analysis of the 26S rDNA D1/D2 region, Z. hellenicus and Candida bertae var. bertae were the closest species with 54 and 56 bp substitutions, respectively. Similar results have been obtained from analysis of the 18S rDNA. All these data support the hypothesis that the yeast, named Candida bituminiphila, is a novel species closely related to Z. hellenicus. The holotype and only isolate of C. bituminiphila is strain CBS 8813T (= MUCL 41424T).

Searching for an explanation for diphthong perception: dynamic tones and dynamic spectral profiles.

The aim was to find a psychophysical explanation for the perception, by naive listeners, of diphthongs as single vowels, even though they are essentially formant movements. Subjects were asked to match sinusoidal tone and resonance glides around 1,000 Hz with two connected steady-state tones or resonances whose frequencies could be controlled independently. The expectation was that short glides (below 120 ms) would give rise to single perceptual events without any movement in a particular direction, so that the two matching steady-state patterns would not show any frequency direction either; long resonance glides (above 120 ms), on the other hand, were expected to be perceived as rising or falling and matched accordingly. The results showed an effect of duration, although it interacted with glide width. At durations shorter than about 120 ms, subjects placed the two steady profiles with which they had to match the dynamic profile closer together than with durations over 120 ms; however, this only occurred if a glide covered more than 500 Hz, and is therefore irrelevant to diphthong perception.

Medical and ground crew support during Euromir 95.

The longest manned mission previously supported by ESA was Euromir 94, which lasted just 30 days. The quantum leap to the originally planned 135 days of the Euromir 95 mission meant that a number of concepts needed to be rethought and adapted. One of the more obvious consequences was that the astronaut would be separated for a much longer period from his home environment, which meant that some of the ground-related support also had to be re-evaluated. Additional support associated with the 'psychological climate' onboard the station as a result of the longer mission duration was also necessary. Post-flight analysis has shown that all support elements functioned satisfactorily, but a number of potential improvements have also been identified.

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.

Chronic ecotoxicity of copper and cadmium to the zebra mussel Dreissena polymorpha.

In order to evaluate ecological consequences of the long-term presence of metals in aquatic ecosystems, we investigated the filtration rate and survival of zebra mussels (Dreissena polymorpha) during chronic exposure to Cu and Cd. The filtration rate was measured once a week in laboratory experiments lasting 9-11 weeks. The lowest Cu concentration tested (13 micrograms/L) did not affect the filtration rate and survival of D. polymorpha, but the lowest Cd concentration (9 micrograms/L) did affect the filtration rate, but had no effect on survival. The EC50 for Cd decreased markedly from 388 micrograms/L to 27 micrograms/L when the exposure time was lengthened from 48 hours to 10 weeks. The largest decrease in EC50 for Cd was observed during the first week of exposure. In contrast, the EC50 for Cu did not decrease with increasing exposure time (chronic EC50: 43 micrograms/L). Since the chronic LC50 for Cd was 130 micrograms/L, the filtration rate appeared to be a far more sensitive endpoint for ecotoxicological laboratory experiments than mortality. D. polymorpha was capable of regulating the body concentration of the essential metal Cu at low concentrations in the water (13 micrograms/L). Cd was accumulated at every Cd concentration in the water, suggesting that Cd could not be regulated by D. polymorpha. It is concluded that the relation between short-term and long-term ecotoxicity was different for each metal and could not be predicted from the results of the short-term experiments.

Biomonitoring of heavy metals in the Western European Rivers Rhine and Meuse using the freshwater mussel Dreissena polymorpha.

Since 1976, active and passive biological monitoring programs using the freshwater mussel Dreissena polymorpha have been carried out to study trends in the bioavailability of heavy metals in the rivers Rhine and Meuse. The Cd concentration in mussels exposed in the river Rhine has decreased from 74 mg kg(-1) in 1976 to 1.5 mg kg(-1) in 1988. In the river Meuse, however, the Cd concentration in Dreissena polymorpha has increased from 6 mg/kg (-1) to 22 mg kg(-1). Cu concentrations in mussels have not changed. Comparison of heavy metal concentrations in mussels from Lake Heerhugowaard, Lake Markermeer, Lake Maarsseveen and the river Dieze demonstrated that background concentrations for Cu, Zn, Cd and Pb in Dreissena polymorpha are about 12, 110, 1 and 0.5 mg kg(-1), respectively. Mussels from these four locations showed seasonal variation in heavy metal concentrations. This may be caused by both changes in the bioavailability of the metals and by the annual growth and reproductive cycle of the mussels. Therefore, one should take care that animals are collected at the same location and in the same section in long-term active biological monitoring programs.