Cycles in the Environment

Did you know that the atoms of carhon, nitrogen, and other elements in your body are far older than you In fact, they ve been around since before life began on Earth. The amount of matter on Earth never changes. As a result, it must be recycled constantly. You learned about the water cycle earlier in the chapter. A number of elements cycle through the environment in similar, distinct pathways. 

Carbon cycles in and out of the environment through many pathways. 

About 25% of the sunlight that strikes Earth s atmosphere is reflected back into space. Most of the remaining 75% is absorbed by atmospheric gases and Earth in the form of heat. 

Carbon dioxide also enters the atmosphere when plants and animals decompose. Recall from Chapter 22 that the remains of ancient plants and animals were converted under pressure to fossil fuels. When fossil fuels are humed, the carbon is converted to CO2. As you ll learn, the huming of fossil fuels and other human activities may he disrupting the balance of the carhon cycle. 

Increases in greenhouse gases such as CO2 lead to corresponding increases in the greenhouse effect. Some scientists have predicted that these increases will cause global temperatures to rise, a condition known as global warming. 

---

The most important concept with respect to arsenic cycling in the environment is constant change. Arsenic is ubiquitous in living tissue and is constantly being oxidized, reduced, or otherwise... 

Natural emission and re-emission processes are particularly important for the mercury cycle in the environment. The distribution of mercury re-emission from soil in Europe is illustrated in Figure 4. The most significant re-emission fluxes are in Central Europe... 

Krapivin V.F. and Potapov 1.1. (2006). Monitoring of the chemical cycles in the environment. Ecological Systems and Devices, 12, 3-11 [in Russian]. 

The mechanism of transport of the majority of pollutants in the environment is, in general, unknown. This transport is often associated with changes in the chemical character and the concentration of individual chemical species in the environment (washing-out, rain-out, metabolism, aging , etc.). The mechanisms of the resulting effects (e.g. damage to the environment) are also unknown. Fig. 1-3 demonstrates part of the heavy metal cycle in the environment where different sources and sinks exist, and these are connected by several different, simultaneous, and sometimes interfering pathways. 

The rise in the production and use of synthetic polymers worldwide was recently estimated at around 140 million tonnes per year, with most of these being petroleum-based and causing an increasing problem both as environmental pollutants and in the pressure they exert as landfill components. Biodegradation and biodeterioration of these materials can play an important role in microbial ecology and nutrient cycling in the environment. Compared to the importance of these materials in the environment, there have been relatively few studies on the colonization. 

Figure 11.1 Pesticide cycling in the environment. (From Edwards, C.A., Crit. Rev. Environ. Control, 1, 7,1970. With permission.)...

Taroncher-Oldenburg, G., Griner, E. M., Francis, C. A., and Ward, B. B. (2003). Oligonucleotide microarray for the study of functional gene diversity in the nitrogen cycle in the environment. Appl. Environ. Microbiol. 69, 1159—1171. 

Nitrogen gas is converted into biologically useful nitrates by nitrogen fixation. Nitrogen is returned to the atmosphere by a cycle in the environment. 

This account is directed almost exclusively to low-molecular-mass xenobiot-ics so that a discussion of biosynthetic reactions mediated by microorganisms and of biopolymers lies beyond its assigned limits. A few brief comments seem justified, however, because of an upsurge of interest in various groups of naturally occurring compounds, the structure of these biopolymers, and their role in carbon cycling in the environment. Attention is therefore drawn to a few of these, some of which may be persistent. 

There are many important groups of macromolecules. A discussion of these lies beyond the expertise of the author, but it seems appropriate to note briefly a few of these groups due to their environmental relevance and since all of them make a contribution to organic carbon cycling in the environment. 

Unraveling mechanisms chemical reactions and cycles in the environment... 

Shaun A. Watmough is Assistant Professor in the Environmental and Resource Studies Department at Trent University. He received his Ph.D. from Liverpool John Moores University in the UK and completed several years of post-doctoral work at Trent University in Canada. His research interests include the effects of pollutants on soils and forests, trace metal cycling in the environment, and acidification of ecosystems. 

In models that are primarily used for quantitatively describing processes relevant to phosphorus cycling in the environment, it would be beneficial to include more mechanistic detail. The following extensions... 

In the life cycle of the products that were based on PCBs, varying amounts of PCBs were released into the environment in the manufacture, use, and disposal period of the product life cycle. In the environment, as in their use, PCBs proved to be very stable, and this became the problem. PCBs did not break down in the environment, and therefore spread and entered the food chain. In the food chain, PCBs were found to build up in the fatty tissue of animals that consumed PCB-contaminated food. This was particularly true of animals at the top of the food chain due to bioaccumulation in the tissue at each level of the food chain and biomagniflcation due to the build up at each step of the food chain. PCB in sufficient concentration are toxic to wildlife. As a result of the adverse environmental impact, PCB production has been halted and several large-scale contamination sites have been remediated. PCB contamination remains a challenge, such as for the fish in the Great Lakes area. 

---