Chitin is an effective sorbent which can be used in environmental monitoring, beyond obvious applications in withholding metal-containing pollutants from wastewater- or nuclear fuel reprocessing flows, since background levels in (purified) chitin are very low except for a few metals (Fe, Cu, Al, Ti, and Zn). Since retention of M^x+ and their complexes on chitin depend on an oxidation state, and to a lesser extent the presence of possible ligands or co-ligands, partition between chitin samples exposed to sediment and those exposed to water can be changed by environmental factors such as local biota producing or absorbing/metabolizing effective ligands such as citrate or oxalate and by changes of redox potential. Thermodynamics are studied via log P, using calibration functions log P vs. 1/r or log P vs. Σσ (sum of Hammett parameters of ligand donor groups) for di- and trivalent elements not involved in biochemical activity (not even indirectly) and thus measuring “deviations” from expected values. These “deviations” can be due to input as a pollutant, biochemical use of certain elements, precipitation or (bio-induced reduction of SO₄²⁻ or CO₂) dissolution of solids in sediment. Biochemical processes which occur deep in sediment can be detected due to this effect. Data from grafted chitin (saturation within ≤ 10 min) and from outer surfaces of arthropods caught at the same site do agree well. Log P is more telling than total amounts retrieved. Future applications of these features of chitin are outlined.

This study compared the ability of the lichen Evernia prunastri, chitin and chitosan to take up Cu²⁺ and Zn²⁺. It was hypothesized that chitin and chitosan have an accumulation capacity comparable to the lichen, so that these biopolymers could replace the use of E. prunastri for effective biomonitoring of Cu and Zn air pollution. Samples of the lichen E. prunastri, as well as chitin (from shrimps) and chitosan (from crabs), were incubated with Cu and Zn solutions at concentrations of 0 (control), 10, 25, 50, 75, and 100 µM and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Metal concentrations accumulated by lichen, chitin and chitosan samples were strongly and linearly correlated with the concentrations in the treatment solutions. The lichen always showed significantly higher accumulation values compared to chitin and chitosan, which showed similar accumulation features. The outcomes of this study confirmed the great effectiveness of the lichen Evernia prunastri for environmental biomonitoring and showed that chitin and chitosan have a lower accumulation capacity, thus suggesting that although these biopolymers have the potential for replacing E. prunastri in polluted areas, their suitability may be limited in areas with intermediate or low pollution levels.

There is strong adsorption of metal ions and their complexes to chitin, which depends on both the oxidation and complexation states of many of the said elements (whereas others display chemical reactions detectable via electrochemical methods while being retained by chitin); thus, ad- and desorption at ambient water concentrations (often in the nMol/L range) are controlled by the presence and photochemical properties (concerning Eu and probably U and Ag) of mainly biogenic organic matter (both DOC and POC, and DON). With chitin forming the outer hull of mobile organisms (animals), this biopolymer is expected to take part in metal distribution in aquatic (limnetic and riverine) ecosystems. Having studied the attachment of many different elements to both crayfish and grafted (marine shrimp) chitin, with the highest accumulations observed in Bi, V, Ni, and LREEs, one should consider secondary biochemical transformations which take place at different water and sediment levels. After chitin had been embedded into sediment, methanogenesis (which requires Ni), Bi, and Sb biomethylations and photodesorption in the illuminated water column will occur if there are appropriate organics, causing the vertical separation of Eu from other REEs, at least during the daytime. Eutrophication will enhance both the production and especially the photooxidation rates of organics in water because phosphorylated sugars and lipids are formed quantitatively within min P, which enter water and undergo Eu-mediated photooxidation much more readily. Another biopolymer, gelatin, acts as an inert matrix-enhancing organic photooxidation product via Eu, producing chemical waves, indicating autocatalysis upon light impact. From the redox-related photodesorption of metal analytes from chitin, both sensors and devices for (light-assisted) electrochemical energy conversion are being developed by our workgroup. The electrochemical determination of adsorption thermodynamics on chitin is thus directly linked to its applications in environmental monitoring and technology.

Chitin (usually derived from aq. arthropods like shrimp Pandalus borealis) acts as a potent metal sorbent in both environmental monitoring and retention applications such as wastewater purification or nuclear fuel reprocessing. Given this established (starting in the 1970s) use of chitin and the fact that adsorption of metal ions/complexes to chitin does increase the currents observed in metal-centered redox couples by a factor of about 10, it is straightforward to conceive self-organized (by adsorption modified by adding certain ligands bridging M and chitin) surface films which exert electrical information processing by means of inner-sphere redox processes. Preliminary work is shown concerning the influence of ligands—including some possibly acting as inner-sphere-transfer agents, like caffeic acid—on metal ion retention by chitin. Another ligand is reported to enhance current flow into electrodes (i.e., electron injection from some reducing cation). These inner-sphere redox processes, in turn, can be controlled by creating or removing a chain of conjugated double bonds, e.g., by Diels–Alder reactions. Devices admitting corresponding reagents in a controlled manner and appropriate array then act as NAND gates, thus being components capable of performing each kind of classical computation. Applications in environmental analysis and “green” computing for simple purposes like electronic keys are suggested. The empirical basis for these conclusions includes studies on the influences of ligand additions on M adsorption (Mn, Ni, several REEs…) on chitin; some of these bridging ligands, like caffeinate and ferulate, can reversibly react with appropriate dienes. At the employed concentrations, distances among adsorbed metal ions are 1–3 nm, meaning that the charge-flow control takes spacer ligands like carotenoids. Practical setups are pointed to, using evidence from ligand-augmented metal ion–chitin interactions, which might combine oxidizing (Ce) and optically address reducing (Eu) metal ions into a framework for coligand-controlled charge flow.

Analyses of mosses and lichens provide some information on the contents of both particulate and dissolved (from hydrometeors including snow and flooding) metal ions and other elements like As and Sb in the local environment. However, this information is compromised by rarity (and thus duly legal protection) of suitable species (particularly lichens) for regular sampling and also by poorly understood mechanisms of binding. Hence, it is crucial to find an alternative that does not harm or kill rare and/or protected organisms for sampling purposes while providing data that can be traced to environmental levels (e.g., metal ions in water) in a comprehensible way. Studying the coordination of aq. metal ions on some biogenic surface which can form ligating bonds to these ions provides such information. The most abundant and thus cheap such biopolymer acting as both a possible ligand and a water- (or environment-)biomass interface is chitin. Data from chitin exposed in either water, common sandy sediments, and ferric gels delivered by Fe-oxidizing bacteria are processed to understand adsorption in quantitative terms depending on local conditions, accounting for observed BCFs >> 1 for certain elements (Bi, V, LREEs). Slopes of functions that describe the increase of retention of some element upon increasing aq. concentrations allow us to construct (a) some function giving BCF by numerical integration, (b) predict the behavior of other elements for which certain parameters guiding complex formation are known as well. It turns out that top sensitivities (maximum BCF- or partition factor) values are reached with different elements depending on the environment the chitin sample was exposed to. PF can extend the detection and determination of many elements below levels directly observable in water or sediments. The detection of fallout radionuclides on chitin is even more sensitive (by a factor of 20–25) because of omitting dilution in workup by direct observation of γ radiation.

In times of increasing demand for resources, processing various waste materials is becoming more economically and ecologically viable. Red mud is a waste material that originates from the bauxite process, also known as the Bayer process. Red mud, due to its high alkalinity and heavy metal content, is often stored in landfills, which can lead to accidents such as those in Brazil or Hungary, especially if the storage takes place above ground. Red mud contains not only iron and aluminum residues but also other economically valuable metals such as manganese, titanium, cadmium, or cobalt. Currently, only 4 million tons of the annual production of 150 million tons are utilized in various industries, which is a relatively small amount. Typically, only the iron content is further processed, leaving other potential resources untapped. Chitin has a high binding capacity for various trivalent and divalent metal ions, making it a suitable material for separating red mud into its components. It has been demonstrated that chitin can effectively remove aluminum, barium, cadmium, cobalt, copper, manganese, iron, nickel, lead, strontium, and various lanthanides from a red mud-like sludge. The elements bound to chitin can be easily removed using wet chemistry. Biologically compatible substances are predominantly used in this process, with few exceptions. The removal of elements from red sludge or other mining wastewater using chitin is a viable alternative to traditional mining methods.