Organochlorine pesticide contamination in sediments from Richards Bay, South Africa: spatial trends and ecotoxicological risks.

The occurrence and distribution of organochlorine pesticides (OCPs) in aquatic systems is a matter of global concern and poses significant toxicological threats to both organisms and human health. Despite the extensive use of OCPs for pest and disease control in southern Africa, relatively few studies have examined the occurrence and toxicological risks of OCP residues in the region. This study investigates the composition, distribution, and potential sources of OCP contamination in sediments from Richards Bay, a rapidly developing industrial port on the northeast coast of South Africa. Surface sediments collected from Richards Bay Harbour and surrounding areas indicate that OCP contamination in the region is widespread. Total concentrations (∑OCP) in surface samples ranged from 135 to 1020 ng g-1, with hexachlorocyclohexanes (∑HCH; 35-230 ng g-1) and dichlorodiphenyltrichloroethanes (∑DDT; 12-350 ng g-1) the dominant contaminant groups detected. Metabolite isomeric compositions indicate that the presence of aldrin and endosulfan likely result from historical agricultural usage, while recent input of γ-HCH, heptachlor, and endrin may be linked to the illegal use of old pesticide stockpiles. Total DDT concentrations were dominated by p,p'-DDT (80 ± 64 ng g-1), which was attributed to its ongoing use in malaria vector control in the region. A 210Pb-dated sediment core revealed that OCP input to the local environment increased dramatically from relatively low concentrations in the mid-1940s (∑OCP, 355 ng g-1) to peak levels (∑OCP, 781 ng g-1) in the 1980s/1990s. An overall decrease in ∑OCP concentration from the mid-2000s is likely related to restrictions on use following the Stockholm Convention in 2004. Despite current restrictions on use, OCP concentrations exceeded sediment quality guidelines in the vast majority of cases, raising concerns for protected estuarine and mangrove habitats in the area, as well as for local fishing and farming communities.

Direct Analysis of Lignin Phenols in Freshwater Dissolved Organic Matter.

A novel approach for the analysis of dissolved lignin in freshwaters is presented. Lignin concentrations in natural water samples are low, and a lignin extraction is usually required to obtain sufficient material for analysis. In this study, the alkaline CuO oxidation, which liberates a set of lignin-derived phenols, is performed directly on 15 mL of water sample in a microwave digestion system, hence reducing the required sample amount and preparation time considerably. These features make the method particularly suitable to study diagenetic changes of dissolved lignin in small-scale laboratory or field experiments. Phenol separation and quantification by gas chromatography tandem mass spectrometry lead to method detection limits between 22.7 and 1260 ng/L for single phenols, which corresponds to minimum lignin concentrations in the range of 8.5 µg/L (Σ8), offering applications for wetland, river, and lake waters with high terrestrial dissolved organic matter inputs. As a general method improvement, we present the addition of EDTA during phenol workup. EDTA binds remaining copper, thereby speeding up sample flow through the solid phase sorbent during phenol extraction and, furthermore, prevents substantial phenol losses, which occur if a water sample contains nitrate. Three natural water samples, a fresh leaf leachate and two humic-rich lake waters, were analyzed by the direct method presented here and in comparison with the established C18 extraction approach. Results show a similar reproducibility of both methods but reveal lower absolute lignin phenol yields in the humic-rich lake water samples upon C18 extraction.

Splitting of Surface-Immobilized Multicompartment Micelles into Clusters upon Charge Inversion.

We investigate a morphological transition of surface-immobilized triblock terpolymer micelles: the splitting into well-defined clusters of satellite micelles upon pH changes. The multicompartment micelles are formed in aqueous solution of ABC triblock terpolymers consisting of a hydrophobic polybutadiene block, a weak polyanionic poly(methacrylic acid) block, and a weak polycationic poly(2-(dimethylamino)ethyl methacrylate) block. They are subsequently immobilized on silicon wafer surfaces by dip-coating. The splitting process is triggered by a pH change to strongly basic pH, which goes along with a charge reversal of the micelles. We find that the aggregation number of the submicelles is well-defined and that larger micelles have a tendency to split into a larger number of submicelles. Furthermore, there is a clear preference for clusters consisting of doublets and triplets of submicelles. The morphology of surface-immobilized clusters can be "quenched" by returning to the original pH. Thus, such well-defined micellar clusters can be stabilized and are available as colloidal building blocks for the formation of hierarchical surface structures. We discuss the underlying physicochemical principles of the splitting process considering changes in charge and total free energy of the micelles upon pH change.

Cavitation engineered 3D sponge networks and their application in active surface construction.

The design of the 3D architecture surfaces with both space- and time-dependent functionality (cell attraction, pH-trigged self-cleaning, antiseptic/disinfection) is in the focus. The innovative story includes: sonochemical surface activation, formation of feedback surface component (pH-responsible micelles), proof of responsive activity (time resolved cell adhesion and bacteria deactivation) and space adhesion selectivity (surface patterning).

Free-standing membranes via covalent cross-linking of polyelectrolyte multilayers with complementary reactivity.

Polyelectrolyte multilayers were prepared by the layer-by-layer (LbL) technique from polyanions bearing aldehyde and polycations with 4-methylpyridinium moieties. The aldol reaction of these complementary reactive groups can be followed by the formation of fluorescent merocyanine dyes, resulting in cross-linked, ultrathin polymer films. The efficient stabilization of the polymer films allows for their intact removal from high surface energy supports, such as glass or surface oxidized silicon wafers, by simple treatment with salt solutions, yielding free-standing membranes. Increasing separation of the reactive polycation and polyanion layers with layers of inert polycation and polyanion analogues only gradually prevents the coupling reaction. From this dependence, polyions assembled in consecutive adsorption layers seem to be able to penetrate into as far as three neighboring layers.