China
Africa
Explore chapters and articles related to this topic
Introduction to Oil Spills and their Clean-up
Published in Ozcan Konur, Petrodiesel Fuels, 2021
Before discussing the actual effects of an oil spill on various elements of the environment such as birds and fish, the types of effects will be discussed (Fingas, 2012; Shigenaka, 2011). Toxic effects are classified as acute or chronic, which refers to the time of effect of the contaminant on an organism. Acute means toxic effects occur within a short period of exposure in relation to the life span of the organism, and are generally the result of exposure to high contaminant concentrations. For example, acute toxicity to fish could be an effect observed within four days of exposure. Chronic means occurring during a relatively long period, usually 10% or more of the life span of the organism, and is generally the result of exposure to low contaminant concentrations. It might take a significant portion of the life span for a chronic toxic effect to be observable, although it could have been induced by exposure to a substance that was normally acutely toxic. Chronic toxicity refers to long-term effects that are usually related to changes in such things as metabolism, growth, reproduction, behavior, or ability to survive.
Elements of Toxicology and Guidelines
Published in T.S.S. Dikshith, and Safety, 2016
Chronic toxicity studies provide information on the long-term health effects of chemical substances. Adverse health effects in exposed animals and subsequent severe damage is known to occur after repeated exposures to low doses over a period of time. The slow accumulation of mercury or lead in the body, or after a long latency period from exposure to chemical carcinogens is an example. Chronic or a prolonged period of exposures to chemical substances also cause adverse effects to animals. The symptoms caused after chronic exposures usually differ from those observed in acute poisoning from the same chemical. In fact, when exposed to low concentrations of chemical substances, as is the case with chronic toxicity studies, the occupational worker and the general public become unaware of such exposures to the chemical substance.
Subchronic Dermal Exposure Studies with Industrial Chemicals
Published in Rhoda G. M. Wang, James B. Knaak, Howard I. Maibach, Health Risk Assessment, 2017
The distinction between subchronic toxicity and acute or chronic toxicity is somewhat indistinct and can be confusing. Acute toxicity generally refers to toxic effects resulting a short time (e.g., less than a week) following a single dose or multiple doses administered within a 24-h period. Chronic toxicity generally involves adverse effects which are the result of continuous exposure or repeated exposures to a toxicant over a significant portion (e.g., greater than 10%) of the lifespan of a given species. Thus, subchronic toxicity falls somewhere between acute and chronic toxicity and distinctions between these two extremes are sometimes subject to debate. To make matters even worse, the term “subacute toxicity” was often used in older toxicology literature to refer to what we now term “subchronic toxicity.” In order to help to eliminate some of this confusion, some regulatory bodies have established working definitions of subchronic exposure and subchronic toxicity. For example, the National Academy of Sciences (NAS)1 defines subchronic exposure as occurring from a few days up to 6 months and the Organization for Economic Cooperation and Development (OECD)2 characterizes subchronic toxicity as adverse effects resulting from repeated daily exposures to a chemical for part (not exceeding 10%) of the life span. In actual practice, most subchronic studies with industrial chemicals are conducted using toxicant exposures of between 2 weeks and 3 months (i.e., 14, 21, 28, or 90 d) in order to comply with test guidelines for the conduct of such studies established by a particular regulatory agency or scientific organization. Translated in human exposure terms, subchronic exposures represent persistent exposures which might occur as a result of process-related occupational exposures, frequent use of a particular product or formulation over a short period, wearing of a required or favorite article of clothing, lot-related exposures of a chronically used substance, military operations, etc.
Removal of arsenic from contaminated water using radiation-induced grafted chitosan: a critical review
Published in Chemistry and Ecology, 2022
As is the only substance known that can cause cancer in humans by both ingestion and inhalation. Exposure to As also causes non-carcinogenic diseases, such as diabetes, hypertension, hepatomegaly, peripheral vascular diseases, respiratory, cerebrovascular and cardiovascular dysfunctions; moreover, arsenic can cause injury to the central nervous system [94]. The significance of arsenic metabolism deals with transformation from a toxic to a less noxious form. This can be tracked by cell accumulation and/or elimination [95]. The absorbed As undergoes biomethylation, so that dimethyl arsenic acid and monomethyl arsenic acid are formed. The analogous acids are less toxics, in comparison, being excreted through urine (about 50%). However, dimethyl arsenic acid is among the main metabolites eliminated by urine, together with a minor amount of unaffected inorganic As. Multiple studies suggest the possibility that methylated arsenicals from metabolitic processes can produce compounds with unique and potentially higher toxicity. High concentrations of arsenic were found in liver and kidneys after severe intoxication [96]. Chronic toxicity leads to accumulation in liver, kidneys, lungs and heart.