Accumulation of copper in the cell compartments of charophyte Nitellopsis obtusa after its exposure to copper oxide nanoparticle suspension

Cu accumulation in the internodal cell of charophyte Nitellopsis obtusa or its compartments was investigated after 3-h-exposure to lethal effective concentrations (8-day LC₅₀) of CuO nanoparticle (nCuO) suspension or CuSO₄ solution, i.e. 100 mg/L nCuO or 3.18 mg Cu/L as CuSO₄. In both cases, the major part of Cu accumulated in the cell walls. The presence of CuO NPs in the cell wall and within the cell was visualized by scanning electron microscope images as well as confirmed by energy dispersive X-ray spectrum data. Although a threefold higher intracellular concentration of Cu was found after treatment with nCuO suspension, 3.18 mg Cu/L as CuSO₄ induced fast and substantial depolarization of cell membrane potential contrary to that of 100 mg/L nCuO. A delayed effect of nCuO on the survival of the cells was also observed. This suggests that internally accumulated Cu was far less active and further supports the hypothesis of delayed toxicity of internalized nCuO NPs to charophyte cells.

Ecotoxicity effects triggered in aquatic organisms by invasive Acer negundo and native Alnus glutinosa leaf leachates obtained in the process of aerobic decomposition

The replacement of autochthonous tree species by invasive ones in coastal zones of freshwater bodies induces additional alteration of hydrochemical and microbiological characteristics due to decomposition of fallen leaves of non-indigenous species, which can lead to ecotoxic response of the littoral biota. Leaves of invasive to Lithuania boxelder maple (Acer negundo) and autochthonous black alder (Alnus glutinosa) lost more than half of biomass and released stable amount of DOC (60-70 mg/L) throughout 90-day mesocosm experiment under aerobic conditions. This, along with the relatively small BOD7 values detected after some variation within the first month confirms effective biodegradation by fungi and bacteria. The ambient water was more enriched with different forms of N and P by decomposing boxelder maple than by alder leaves. During the first month, both leachates were more toxic to charophyte (Nitellopsis obtusa) at mortality and membrane depolarization levels, while later to two crustacean species. Biomarker response, H(+)-ATPase activity in membrane preparations from N. obtusa, was stronger for A. negundo. Generally, boxelder maple leaf leachates were more toxic to tested hydrobionts and this coincides with previous study on leaves of the same pair of tree species conducted under microaerobic conditions (Krevš et al., 2013).

Toxicity of copper oxide nanoparticle suspensions to aquatic biota

Toxicity effects induced by nanosuspensions of CuO (<50 nm; Sigma-Aldrich) on macrophytic algae cells of Nitellopsis obtusa (96-h median lethal concentration [LC50]), microphytic algae Chlorella (30-min median inhibitory concentration [IC50]), shrimp Thamnocephalus platyurus (24-h LC50), and rotifer Brachionus calyciflorus (24-h LC50) were investigated. No substantial differences between the effects of nonsonicated and sonicated nCuO suspensions were observed. The particle size distribution analysis accomplished by the laser diffraction technique at suspension concentration from 3 to 100 mg/L revealed rapid (within 5 min) reagglomeration of the particles after the sonication. The observed adverse effects on N. obtusa cells may be attributed to nanoparticles per se, but not to ionic Cu, because neither chemical analysis nor biological testing (algae survival in the supernatants of suspensions) confirmed the presence of cupric ions in toxic amounts. Contrary to ionic Cu form, nCuO delayed the initial phase of N. obtusa cell membrane depolarization. Lethality tests with rewash demonstrated that the least used 5-min exposure in 100 mg/L nCuO sonicated suspension induced 70% mortality in charophyte cells after 8 d, whereas the rewash after a short exposure to a noticeably toxic concentration of Cu(2+) prevented cell mortality. The obtained data suggested the possible influence of a thick charophyte cell wall on the dynamics of nanotoxicity effects.

Leachate toxicity assessment by responses of algae Nitellopsis obtusa membrane ATPase and cell resting potential, and with Daphtoxkit F magna test

A microscale bioassay based on 50% inhibition of K(+), Mg(2+)-ATPase activity in a microsomal fraction isolated from Nitellopsis obtusa cells was developed. Compared to that for a plasma membrane fraction purified in a sucrose gradient, the preparation procedure for a microsomal fraction is less time consuming and the yield is substantially higher. Characteristics of the microsomal preparation proved to be similar to those of the highly purified plasma membrane preparation (Manusadzianas et al., 2002), at least for heavy metals. Sensitivity to CuSO(4) of the frozen (-8 degrees C) microsomal fraction [49 +/- 17 (SD) microM; n = 8] did not significantly differ from that of the freshly isolated one (52 +/- 30, n = 8), at least for 40 days. Toxicity of leachate water from Kairiai (northern Lithuania) solid waste landfill was assessed by taking samples from various points including temporary reservoirs and analyzing them immediately after spillage (summer 2002) and after storage for almost 2 years at 4 degrees C-6 degrees C. Two tests with the macrophytic alga Nitellopsis obtusa (Charatox, 45-min EC(50) of resting potential depolarization, and ATPase assay, IC(50) of membrane ATPase activity) and one test with the crustacean Daphnia magna (Daphtoxkit F, 48-h 50% immobilization) tests were used. In general, all three tests showed successively decreasing values of landfill leachate toxicity with an increasing degree of dilution with surface waters. The possibility of employing preserved algal preparations on demand in test batteries seems to be promising, especially in emergencies.

Response of the charophyte Nitellopsis obtusa to heavy metals at the cellular, cell membrane, and enzyme levels

The responses of the freshwater macroalga Nitellopsis obtusa to heavy metal (HM) salts of Hg, Cd, Co, Cu, Cr, and Ni were assessed at different levels: whole-cell mortality (96-h LC(50)), in vivo cell membrane (45-min depolarization of resting potential, EC(50)), and enzyme in plasma membrane preparations (K+, Mg2+-specific H+-ATPase inhibition, IC(50)). To measure ATPase activity, a novel procedure for isolation of plasma membrane-enriched vesicles from charophyte cells was developed. The short-term ATPase inhibition assay (IC(50) from 6.0 x 10(-7) to 4.6 x 10(-4) M) was slightly more sensitive than the cell mortality test (LC(50) from 1.1 x 10(-6) to 2.6 x 10(-3) M), and the electrophysiological test with the end point of 45-min depolarization of resting potential was characterized by less sensitivity for HMs (EC(50) from 1.1 x 10(-4) to 2.2 x 10(-2) M). The variability of IC(50) values assessed for HMs in the ATPase assays was close to that of LC(50) values in the mortality tests (CVs from 33.5 to 83.5 and from 12.4% to 57.7%, respectively), whereas the EC(50) values in the electrophysiological tests were characterized by CVs generally below 30%. All three end points identified two separate HM groups according to their toxicity to N. obtusa: Co, Ni, and Cr comprised a group of less toxic metals, whereas Hg, Cu, and Cd comprised a group of more toxic metals. However, the adverse effects within each group were discriminated differently. For example, the maximum difference between the highest and lowest LC(50) for the group of less toxic metals in the long-term mortality test was approximately 60% of the response range, whereas the corresponding difference in IC(50) values in the ATPase assay was 30%. In contrast, the LC(50) values of the more toxic metals occupied only 10% of the response range, whereas the IC(50) values were spread over 70%. Further investigation should be done of the underlying mechanism or mechanisms responsible for the observed differences in the dynamic range of a particular end point of the groups of toxicants of varying strength.

Repair of a defect following the removal of a maxillary adenomatoid odontogenic tumor using guided tissue regeneration. A case report

Adenomatoid odontogenic tumors (AOT) make up 3% of odontogenic tumors. This tumor, most commonly found in the maxillary arch, mimics a follicular cyst associated with an impacted tooth. This is a case report of an AOT found in a 14-year-old female undergoing active orthodontic therapy. The surgical removal of the lesion resulted in the exposure of a large bony cavity surrounding the maxillary left canine. Placement of freeze-dried bone and coverage with an expanded polytetrafluoroethylene membrane resulted in rapid and complete healing of the lesion and restoration of osseous support.