Nutrients metal availability/toxicity

From a practical standpoint, stream fulvic acids which comprise over 90% of the stream humic substances are not an important food source for aquatic organisms, but all stream humic and fulvic acids are positive influences on biological growth in respect to phosphorus and nitrogen nutrient cycling, trace metal availability, and limiting potential metal toxicity. 

Trace metals can serve as essential nutrients and as toxic substances. For example, cobalt is a component of vitamin B12. This vitamin is essential for nitrogen-fbdng algae. In contrast, copper is toxic to marine phytoplankton at free ion concentrations similar to those found in seawater (Sunda and Guillard, 1976). The possibility that iron availability may limit primary productivity was discussed earUer. 

Biological extractions are carried out to determine if biologically important elements are at levels that are sufficient, yet not toxic, for plant needs. Acid soil extraction to determine the biologically available plant nutrients is the most common type of extraction of soil carried out. The objective is to extract a portion, not all, of a particular nutrient or metal that is correlated to the amount available to plants. The plants of primary interest are crop plants such... 

In some cases, resins have been used to try to determine only the plant or more generally the biological availability of an ionic species. Resins placed in soil have also been used to study ion speciation, soil microbiology, various phosphorus measurements, soil nutrient supply rate, nutrient transformations and movement, and micronutrient and metal toxicity [22-25],... 

Plants are living organisms with physical requirements that are often in conflict with the nature of the pollutant or the industrial setting to be remediated. These requirements can include soil pH, soil texmre, and available nutrients. Hybrid poplars are reasonably tolerant of organic compounds, but high concentrations of metals, salts, and ammonia are toxic. Phytoremediation is also a slower process than alternative technologies, and cleanup often requires several growing seasons. 

The vegetation used to extract toxic metals may pose a risk to animals that consume these plants. Animal consumption of process plants could also result in harmful metals working their way up the food chain. Hyperaccumulation is a much slower process than most chemical and physical technologies, and its performance is typically measured in months or years. Technology effectiveness is limited by root growth thus, wastes must be relatively close to the surface. In addition, the toxicity of the targeted contaminants and other site-specific characteristics such as pH, soil characteristics, nutrient content, and water availability can impact technology performance. 

Several elements, particularly zinc and copper, could play a role as trace nutrients for phytoplankton. They are known to be important for growth of terrestrial plants, but neither the requirement for these nutrients nor the elemental distributions in seawater are well known. The biological availability of both zinc and copper is controlled by their complexation with organic material. Analytical methods that have the distinction of being able to discriminate chemical forms of the metal are needed. These measurements reflect the chemical reactivity and biological availability or toxicity of the metal more accurately. 

Fractions of higher molecular mass, which are mostly insoluble, can withhold large amounts of metals, especially in alkaline environments. Metals are thus subtracted from precipitation and subsequent crystallization, processes that would decrease their availability (Schwertmann, 1966), and a reserve of micro-nutrients is created which is in equilibrium with complexing molecules. On the other hand, under conditions of high metal concentrations, complexation by humified organic matter may limit the amount of metals in solution under these conditions, interchain bonds may form, with possible precipitation of humic molecules. This process can be important for toxic elements, the activity of which can thus be reduced to nontoxic levels (Gerke, 1992). 

Salinity affects microbial activity, in part, because it controls water availability. The higher the salinity, the more energy an organism must expend to maintain a favorable osmotic balance. Salts, of course, have effects on living organisms beyond water availability. For example, salts can be both a source of essential nutrients as well as a source of toxic heavy metals. Also, sulfate salts appear to be more favorable for life than chloride salts see the discussion in Sect. 5.1.2 (Aqueous Saline Environments). However, in this section on salinity, the focus will be on salinity as a control on water availability. 

The inorganic characterization schedule for wastewaters to be treated using biological systems should include those tests which provide information concerning (/) potential toxicity, such as heavy metal, ammonia, etc (2) potential inhibitors, such as total dissolved soHds (TDS) and chlorides 3) contaminants requiring specific pretreatment such as pH, alkalinity, acidity, suspended soHds, etc and (4) nutrient availability. 

Adsorption is an important process in many industrial, biological, and environmental systems. One compelling reason to study adsorption phenomena is because an understanding of colloid stability depends on the availability of adequate theories of adsorption from solution and of the structure and behavior of adsorbed layers. Another example is the adsorption of pollutants, such as metals, toxic organic compounds, and nutrients, onto line particles and their consequent transport and fate, which has great environmental implications. Often, these systems are quite complex and it is often favorable to separate these into specific size for subsequent study. 

Sulfur cycling is affected in a variety of ways, including UV photoinhibition of organisms such as bacterioplankton and zooplankton that affect sources and sinks of DMS and UV-initiated CDOM-sensitized photoreactions that oxidize DMS and produce carbonyl sulfide. Metal cycling also interacts in many ways with UVR via direct photoreactions of dissolved complexes and of metal oxides and indirect reactions that are mediated by photochemically-produced ROS. Photoreactions can affect the biological availability of essential trace nutrients such as iron and manganese, transforming the metals from complexes that are not readily assimilated into free metal ions or metal hydroxides that are available. Such photoreactions can enhance the toxicity of metals such as copper and can initiate metal redox reactions that transform non-reactive ROS such as superoxide into potent oxidants such as hydroxyl radicals. 

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