Organic chemicals, number toxicity

A similarity-related approach is k-nearest neighbor (KNN) analysis, based on the premise that similar compounds have similar properties. Compounds are distributed in multidimensional space according to their values of a number of selected properties the toxicity of a compound of interest is then taken as the mean of the toxicides of a number (k) of nearest neighbors. Cronin et al. [65] used KNN to model the toxicity of 91 heterogeneous organic chemicals to the alga Chlorella vulgaris, but found it no better than MLR. 

PVDC is currently handicapped by the ecological problems associated with chlorine, the limited number of producers, its cost, limited resistance to light and some organic chemicals such as aromatic hydrocarbons, ketones etc., impact sensitivity the more so as the temperature decreases, high density, fume toxicity and corrosivity in the event of fire. 

Both Congress and EPA have a number of studies and efforts underway which may ultimately impact disposal of pesticide waste. Among these are reevaluation of the small generator exclusion limit, expansion of Extraction Procedure toxicity characteristic to include additional organic chemicals, revamping of Section 261. 33 (commercial chemical products which are hazardous waste when discarded or intended to be discarded) to both bring mixtures of active ingredients under the definition and also to establish concentration thresholds for the wastes, and a prohibition on land disposal of certain wastes. At this time I would like to briefly touch on each of these areas. 

Chemical injuries to the liver depend on the type of toxic agent, the severity of intoxication, and the type of exposure, whether acute or chronic. The six basic types of liver damage are fatty liver, necrois, hepatobiliary dysfuntions, viral-hke hepatitis, and (on chronic exposure) cirrhosis and neoplasia. A number of organic chemicals and drugs induce fatty liver and hver necrosis. 

NOTE Chlorine is widely used in the protection of drinking water, the manufacture of pharmaceuticals, crop pesticides, paper, rubbers, resins and plastics, and thousands of other products. Nevertheless, since the early 1990s, there has been a groundswell of opinion to either ban or severely limit the use of chlorine in all manners of processes. This is based on observations associated with the probable adverse effect to the environment from certain chlorinated organic chemicals, such as polychlorinated biphenyl (PCB) and the insecticide DDT. There is also concern in a number of other areas, for example, that free chlorine may contribute to effluent toxicity due to the formation of chloramines and trihalomethanes (THMs). In the United States in 1993 to 1994, this opinion was fueled by the possibility that the Environmental Protection Agency (EPA) would... 

Given the enormous number of toxicants, it is difficult to classify them chemically, either by function or by mode of action, since many of them would fall into several classes. Some are natural products, many are synthetic organic chemicals of use to society, while others are by-products of industrial processes and waste disposal. It is useful, however, to categorize them according to the expected routes of exposure or according to their uses. 

Structural descriptors are implemented extensively in the development of prediction models for a large number of endpoints related to the fate and toxicity of organic chemicals in the environment and to human health. The TIs were reported for the modeling of properties of the pure substances such as boiling point (Basak et al., 1996), vapor pressure (Liang and Gallagher, 1998) and water... 

---