🗊Презентация Persistent organic pollutants

Lecture №3 Persistent organic pollutants (POPs)

Persistent organic pollutants Persistent organic pollutants (POPs) are organic compounds that, to a varying degree, resist photolytic, biological and chemical degradation. POPs are often halogenated and characterised by low water solubility and high lipid solubility, leading to their bioaccumulation in fatty tissues. They are also semi-volatile, enabling them to move long distances in the atmosphere before deposition occurs.

Persistent organic pollutants

Persistent organic pollutants have four key characteristics in common: 1. Persistent organic pollutants are TOXIC, 2. POPs are ENVIRONMENTALLY PERSISTENT. 3. POPs resist breakdown in water but they are soluble in fatty tissue, which makes them bioavailable to mammals. 4. POPs are semi-volatile and thus are capable of TRAVELLING GREAT DISTANCES through cycles of evaporation and atmospheric cycling and deposition (referred to as the "grasshopper effect"). 5. POPs are volatile at warm temperatures and condense at cooler temperatures, reaching their highest concentrations in the cooler regions of the world (northern latitudes and high altitudes). 6. Synthetic (man-made) organic chemicals POPs have been found on every continent on the planet, and in every major climatic zone, including the world's most remote regions, such as the open ocean and deserts, and in every wildlife species and human being.

Persistence time for some selected pesticides

The POPs are: Lipophilic – they have a tendency to remain in fat-rich tissues. Highest levels found in marine mammals – immune dysfunction is considered as a plausible cause for increased mortality among marine mammals. Acute, high-level toxicity is well characterized – acute effects after high-level exposure have been described for some of the organochlorine pesticides (e.g. aldrin, dieldrin and toxaphene). PCBs have caused welldocumented episodes of mass poisoning called "Yusho" and "Yu Cheng“, that occurred in China, Province of Taiwan, and in Japan.

Groups of POPs POPs are generally divided into two groups according to their sources: they are either intentionally produced for one or more purposes or they are accidentally formed in production or combustion processes

1. Intentionally produced chemicals The group of intentionally produced chemicals can further be divided into two groups: Organochlorine pesticides. The organochlorine pesticides were developed in the 1940s and 1950s and widely used until the 1970s and 1980s, where most of them where restricted or banned and they are now to a large extent replaced with less persistent products. Industrial compounds The group of chlorinated industrial compounds includes the polychlorinated biphenyls (PCBs), consisting of 209 different congeners with different degree of chlorination.

2. Accidentally formed chemicals The main classes of unintentionally by-products are: the polychlorinated dibenzo–p–dioxins (PCDDs), the polychlorinated dibenzofurans (PCDFs) The PCDD/Fs consist of 75 and 115 different congeners respectively, which are formed as by-products during chlorination processes and combustion.

2. Accidentally formed chemicals and the polycyclic aromatic hydrocarbons (PAHs).

Persistent organic pollutants The Stockholm Convention on Persistent Organic Pollutants (May 2001) focuses on reducing and eliminating releases of 12 POPs (coined the "Dirty Dozen” by the United Nations environment Programme (UNEP) http://chm.pops.int/default.aspx

The twelve priority persistent organic pollutants listed under the Stockholm Convention.

Criteria for identification of ‘new’ POPs under the Stockholm Convention (2001)

Characteristics of POPs The definition of persistence is that the half-life in water is greater than two months or the half-life in soil or sediments is greater than six months or that there is other evidence that the chemical is sufficiently persistent to be of concern. A compound bioaccumulates if the logarithm of the octanol-water partition coeffcient (logKow) is greater than 5 or if the bioconcentration factor (BCF) or the bioaccumulation factor (BAF) is greater than 5000 or if there is other evidence that the chemical bioaccumulates.

Characteristics of POPs There is potential for long-range transport if the half-life of a compound in air is greater than two days or if it is detected in remote regions. If there is evidence of adverse effects or indications of potential damage to human health or the environment a compound is said to be toxic. Observed adverse effects are e.g. effects on the reproduction, development and the immune system and the promotion of tumors.

Characteristics of Arctic ecosystems related to POP accumulation. 1. Cold 2. Conspicuous species and humans at high trophic levels Arctic food chains, in general, are neither longer nor shorter than natural food chains in temperate regions. There are many species of first-level carnivores in both 3. Low species diversity 4. Low productivity 5. Cyclic annual productivity Arctic ecosystems are highly pulsed due to fluctuations in light levels, nutrient input, and temperature. OCs and nutrients deposited on 6. Physical stressors in the Arctic

Transport of POPs in the environmental compartments The atmosphere is the fastest environmental transport path, and most POPs are believed to enter the Arctic through the air. It can take a few days or weeks for the air from source regions to reach into the Arctic. Pollutants are also transported in the oceans by the ocean currents. Although the transport is slow, it can be important depending on the partitioning into water compared to the partitioning into air. Soil is a stagnant medium, so there is no horizontal transport of POPs in soil. Partitioning into the water within the soil and subsequent run-through can though lead to transport of POPs within the soil. A recent model study has suggested that vertical movement of chemicals sorbed to soil particles, by e.g. bioturbation, cryoturbation and erosion into cracks in dry soil is of importance for the environmental fate of POPs Fresh water transport through major rivers is considered to be an important sourceof contamination of the Arctic Ocean. Sea ice may also be a mean of POPs re-distribution. POPs sorbed to particles bound to sea ice can be transported out of the Arctic Ocean to melt regions in the Fram Strait. Another transport pathway that may be of importance for the transport into the Arctic is through migratory animals, e.g. seabirds, cetaceans, salmons, and Arctic cods.

Contaminant sources can be provisionally separated into three categories: Distant sources: Located far from receptor sites in the Arctic. Contaminants can reach receptor areas via air currents, riverine flow, and ocean currents. During their transport, contaminants are affected by the combined effects of physical and chemical factors. Persistence in the environment is, therefore, one of the most important characteristic in determining the ability of contaminants to reach the Arctic. In this respect, PTS, due to their low degradation rates, are often considered to be ‘global contaminants’ subject to long-range transportation.

Sector share of PAH emissions (EEA member countries)

 Estimated Percent Contribution of Sector Dioxins and Furans Releases to the Atmosphere (1999)

Exchange of POPs between the environmental compartments In the air POPs can associate with particles. Contaminated water can run through soil into a fresh water compartment and from there through rivers into the ocean. Finally, POPs are uptaken by animals.

Reactions with other environmental constituents In air there are mainly two types of reactions: photolysis and oxidation. Photolysis happens when chemical reactions or rupture of chemical bonds are sparked by the energy in sun light. The main oxidation of POPs are reactions with OH·, but there can also be reaction with other radicals, such as the nitrate (NO3-) radical and ozone (O3). In water POPs are subject to hydrolysis, a process in which the compounds reacts with water, hydrogen ion or hydroxyl ion. Finally, POPs undergo biodegradation, which occur in both water and soil. This term covers a wide range of processes in microbial organisms.

Environmental fate of POPs According to the global fractionation hypothesis' differences in volatility arising from different physical-chemical properties (especially the vapour pressure) leads to different atmospheric transport distances, and thereby a fractionation of the compounds

Environmental fate of POPs POPs are deposited to the surface through either wet or dry deposition. On the ground, POPs may be sorbed onto the surface of vegetation or soil or be dissolved in water. If the temperature rises, the surface-sorbed or dissolved POPs may re-volatilise into the atmosphere due to their temperature dependent physical-chemical properties, and here they can undergo further atmospheric transport. This effect is termed the `grasshopper effect'.

`grasshopper effect'

Environmental fate of POPs The temperature dependence of the volatility has another effect. When POPs reach cold environments such as the Arctic the low temperatures make it diffcult for them to escape the region and they are thus `trapped'. This phenomenon has been named `cold condensation'. This is due to the relatively small size of the Arctic as a whole and especially of the environmental organic phases with capacity of retaining POPs. Measurements have shown that mountain regions also can act as cold traps of POPs.

Biomagnification of DDT in the food web.

Major Sources of Human Exposure