Marine microalgae (Emiliania huxleyi) were grown in seawater enriched only with nitrogen and phosphorus, without control of free metal concentrations using synthetic chelators. Complexing ligands and thiol compounds were determined by cathodic stripping volt-ammetry. Copper was added to these cultures, and ligands were produced in response to the copper addition. Parallel measurements of thiols showed that glutathione and other unidentified thiols (electrochemically similar to thioacetamide) were produced by the algae at rates and concentrations similar to those of the complexing ligands. Smaller amounts of thiols were produced when ligands including thiols were added to the culture. The results indicate that thiols can account for a major part or most of the copper-complexing ligands produced by these algae. Furthermore, a feedback mechanism exists in which the production of thiol-type complexing ligands is controlled by the free copper concentration, production already being stimulated by an increase of [Cu 2ϩ ] from 0.4 to 1.5 pM. Incubations with added exudates, thiols, and salicylaldoxime (SA) showed much reduced copper toxicity even though copper uptake was increased by the exudates and the SA.Culture experiments have shown that marine and freshwater phytoplankton release complexing ligands into culture medium (e.g., van den Berg et al. 1979;Imber and Robinson 1983), which may be important because the availability of metals to algae is known to depend on their chemical composition (e.g., Brand et al. 1983). Therefore, the interaction of phytoplankton with trace metals is reciprocal: the biota affect the trace metal chemistry and the trace metals affect the biota.Using marine algal cultures where the metal chemistry was controlled by a synthetic chelator (usually ethylenediaminetetraacetic acid [EDTA]), the biological uptake of copper has been shown to be related to the cupric ion concentration, [Cu 2ϩ ] (e.g., Brand et al. 1986); toxicity occurs at pM levels of Cu 2ϩ . The concentration of Cu 2ϩ is typically lowered by by 2-3 orders of magnitude by organic complexation in seawater to a [Cu 2ϩ ] of 0.03-0.3 pM, which is thought to be sufficiently high to meet algal nutritional requirements but is below copper toxicity levels (Sunda 1995).

De‐Deus G, Brandão MC, Leal F, Reis C, Souza EM, Luna AS, Paciornik S, Fidel S. Lack of correlation between sealer penetration into dentinal tubules and sealability in nonbonded root fillings. International Endodontic Journal, 45, 642–651, 2012. Abstract Aim  To determine the correlation between leakage and sealer penetration into dentinal tubule. Methodology  The root canal of 60 mandibular central incisor teeth were prepared and filled under standardized conditions. Teeth were placed into a device to assess glucose penetration using 15 psi pressure application. After 1 h, glucose concentrations in the lower chamber were measured using an enzymatic reaction. Each specimen was then sectioned horizontally at 3, 6 and 8 mm from the apex, and a standard metallographic preparation was performed. The coronally facing surface of each slice was examined in a high‐resolution stereomicroscope and under Confocal Laser Scanning Microscope. For each slice, the external outline of the root canal, the internal circumference of the root canal walls and the areas along the canal walls where the sealer had penetrated into the dentinal tubules (sealer tags) were outlined and measured. Afterwards, the percentage of the sealer penetration in each section was calculated. The Spearman correlation test was used to verify the correlation between the variables studied (glucose leakage and sealer penetration into dentinal tubules). Results  The means and standard deviations of glucose leakage were 0.744 g L−1 (±0.5), and the percentage of the dentinal tubule sealer penetration varied between teeth from 5.6% to 42.21%, with an average of 13.7 ± 17.2%. The Spearman correlation test revealed no significant correlation between the two factors analysed (P = 0.082). The r2 value was equal to 0.12. Conclusions  There was no significant correlation between sealability sealer penetration into dentinal tubles. The lack of correlation reported is of relevance as sealer penetration into dentinal tubules has been used as an advantageous property during the launch of new root filling materials and techniques.

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