We developed an inductance-based valvometry technique as a detection system to measure the valve daily activity in freshwater clam Corbicula fluminea in response to waterborne arsenic. Our findings reveal that C. fluminea experiences a valve opening in the absence of arsenic predominantly in the morning hours (03:00-08:00) with a mean daily opening/closing period of 21.32 (95% CI: 20.58-22.05) h. Amplification of daily activity occurred in the presence of arsenic. Behavioral toxicity assays revealed arsenic detection thresholds of 0.60 (95% CI: 0.53-0.66) mg l(-1) and 0.35 (95% CI: 0.30-0.40) mg l(-1) for response times of 60 and 300 min, respectively. The proposed valve daily activity model was linked with response time-specific Hill dose-response functions to predict valve opening/closing behavior in response to arsenic. The predictive capabilities were verified satisfactory with the measurements. Our results implicate a biomonitoring system by valve daily activity in C. fluminea to identify safe water uses in areas with elevated arsenic.
Arsenic is a potent human carcinogen of skin, lung, and urinary bladder. Freshwater clam Corbicula fluminea is a commercially important native species in Taiwan. C. fluminea is also a suitable biomonitoring test organism. Little is known, however, about the actual effects of arsenic on C. fluminea. The objectives of this study were to provide information on the acute toxicity and bioaccumulation kinetics of arsenic in C. fluminea. We carried out a 14-day exposure experiment to obtain bioaccumulation parameters. Uptake was very rapid when C. fluminea was first exposed and then slightly decayed during the uptake phase of the experiment and an uptake rate constant of 1.718 +/- 6.70 (mean +/- SE) mL g(-1) d(-1) was estimated. The elimination of arsenic from C. fluminea obeyed first-order depuration kinetics (r(2) = 0.85, p < 0.05) with a calculated half-life of 6.80 days. The derived bioaccumulation factor of 16.84 suggests that arsenic has a high potential for bioaccumulation in C. fluminea. This had important implications for dietary exposure of arsenic to humans who eat contaminated clams, because the soft tissue usually constitutes the majority of tissue consumed. The 96-h LC50 value was estimated to be 20.74 (95% CI: 11.74-30.79) mg L(-1) obtained from a 7-day acute toxicity bioassay. We also kinetically linked an acute toxicity model and a Hill sigmoid model to reconstruct an internal effect concentration based dose-response profile to assess the effect of soft tissue arsenic burden on the C. fluminea mortality. This result could be used to support the establishment of an ecological risk assessment to prevent possible ecosystem and human health consequences.
There are many bioindicators. However, it remains largely unknown which metal-bioindicator systems will give the reasonable detection ranges of bioavailable metals in the aquatic ecosystem. Various experimental data make the demonstration of biomonitoring processes challenging. Ingested inorganic arsenic is strongly associated with a wide spectrum of adverse health outcomes. Freshwater clam Corbicula fluminea, one of the most commonly used freshwater biomomitoring organisms, presents daily activity in valve movement and demonstrates biotic uptake potential to accumulate arsenic. Here, a systematical way was provided to dynamically link valve daily activity in C. fluminea and arsenic bioavailability and toxicokinetics to predict affinity at arsenic-binding site in gills and arsenic body burden. Using computational ecotoxicology methods, a valve daily rhythm model can be tuned mathematically to the responsive ranges of valve daily activity system in response to varied bioavailable arsenic concentration. The patterned response then can be used to predict the site-specific bioavailable arsenic concentration at the specific measuring time window. This approach can yield predictive data of results from toxicity studies of specific bioindicators that can assist in prediction of risk for aquatic animals and humans.
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