The biological cycle

It was seen in Chapter 1 that the commodity hydrocarbon polymers which constitute the bulk of the synthetic packaging materials are not indefinitely stable in the environment. However, they are stable enough to constitute an environmental nuisance when they appear as litter or when they have to be disposed of as household or industrial waste. 

One initial response of scientists to this challenge was to design new polymers for packaging applications with chemical structures as close as possible to nature s building blocks namely derivatives of carbohydrates, polyamides and polyesters. Examples of this approach are discussed elsewhere in this book 

The durability in use and reuse of the hydrocarbon polymers and their performance during recycling can be readily controlled. Since the catabolic enzymes cannot biodegrade polymers in the inhospitable hydrophobic environment at the polymer surface, oxidatively resistant hydrocarbon polymers are essentially non-degradable. As was seen in Chapter 9, extensive modification of the polymer surface is a prerequisite to biological attack. In particular, both thermal and photooxidation can be employed to provided a suitable surface environment for microbial colonization and the rate at which these processes occur can be controlled by the use of the appropriate antioxidants and stabilizers [7]. Photooxidation of the hydrocarbon polymers is particularly relevant to the control of litter, whereas thermal oxidation is a prerequisite for aerobic composting. 

---

Almost all elements in the periodic table are involved in at least one way or another in the biological cycle of the ocean. Many elements are essential or required nutrients. Others are carried along as passive participants. In either case the rates of biological processes need to be known. 

The global nitrogen cycle is often referred to as the nitrogen cycles, since we can view the overall process as the result of the interactions of various biological and abiotic processes. Each of these processes, to a first approximation, can be considered as a self-contained cycle. We have already considered the biological cycle from this perspective (Fig. 12-1), and now we will look at the other processes, the ammonia cycle, the cycle, and the fixation/denitrification cycle. 

The biological cycle of arsenic in the surface ocean involves the uptake of arsenate by plankton, the conversion of arsenate to a number of as yet unidentified organic compounds, and the release of arsenite and methylated species into the seawater. Biological demethylation of the methyl-arsenicals and the oxidation of arsenite by as yet... 

The biological cycle — that may encompass processes of biological transformation, plant uptake, bioaccumulation, soil organisms transformations and others. 

In this cycle the reaction of H2 + C02 to give reduced carbon-based fuels such as sugar or oil with oxidation back to H20 and C02 could be useful. It is then precisely the same as the biological cycle. Note that at present mankind and organisms utilise... 

To what extent, and at what rate, do they become involved in the biological cycle, either... 

However, only the smallest part of soluble metals is involved in the biological cycle. Most of these are either lost to water runoff, or retained in the peat organic matter. The latter is the source of gradual remobilization but the whole mineralization may last up to 50 years or even more. The total accumulated retained amount of macro-or trace metals in organic matter of peat is tens and hundreds of time higher than the concentration of annually released soluble forms, which are available for plants. 

C/12C ratio in natural vanillin is smaller than that observed in synthetic vanillin. The same effect applies to glucose, whose isotopic carbon distribution varies depending on the biological cycle of the plant. 

The biological cycle covers all biophyllic elements and vitally important microelements and is characterized by selection of the lightweight isotopes of carbon, hydrogen, nitrogen, and sulfur from heavier forms. 

Bazilevich N.I. and Rodin L.E. (1967). The map-schemes of productivity and of the biological cycle of the most significant types of land vegetation. Bulletin of the All-Union Geographical Society, 99(3), 190-194 [in Russian]. 

Ben Chekroun, M., Amzile, J., Mokhtari, A., el Haloui, N.E., Prevost, J., and Fontanillas, R., Qualitative and quantitative development of carbohydrate reserves during the biological cycle of Jerusalem artichoke (Helianthus tuberosus L.) tubers, N.Z. J. Crop Hort. Sci., 22, 31-37, 1994. 

Inputs of agricultural fertilizers are having more than one impact on the biological pump. A shift in the NO PO4 Si(OH)4 of natural waters is causing a shift in the phytoplankton community structure that should impact the biological cycling of carbon in aquatic systems (Conley et al, 1993). Additionally, a recent shift in the C N P ratios of deeper waters and an increase in export production have been observed for the northern hemisphere oceans (Pahlow and Riebesell, 2000). 

Once inside the cell, HCO3 is converted to CO2 by the enzyme, carbonic anhydrase. CO2 is then fixed by carboxydismutase and OH is excreted to maintain ionic balance. Carbonic anhydrase is also associated with the extracellular carbonate dissolution by boring organisms (Schneider, 1976) and with the C02-transfer system for intracellular calcification. It represents a key enzyme in the biological cycling of carbonate (Degens, 1976 Raven, 1974). 

Biological calcification and the biological cycle of carbonates control the availability of CO2 and its storage in sediments and rocks. These in turn have a strong influence on climatic and other properties of the natural environment. 

The study of the concentration level and distribution of trace metals appears to be of great interest, because these chemical species, mainly deriving from natural sources, play an important role as micronutrients in the biological cycles. 

Until now the attainment of these results was not possible, as few data are available to describe the trace metal concentrations in the Southern Ocean (5-11). In order to contribute to the knowledge of the distribution of trace elements and of the biological cycles in Antarctica over the past twelve Italian expeditions, attention was focused, among others, on trace metals in solid and in dissolved phases (12 29). 

Figure 8.2 Schematic representation of the biological cycle for a metal in nature. All metals essential, and contaminating, have such cycles that are very chemical speciation-dependent (after KJ. Irgolic).

---