Xenobiotics in water and soil surfaces

In many, but not all cases, even the xenobiotic compounds, which have the potential to undergo direct photolysis because they absorb solar light, are degraded faster, when sensitizers are present in the system. One of many examples is given in Table 1. Although the direct photolysis experiments were carried out with monochromatic UV-B light (300 nm), Table 2 shows that the direct plus indirect photolysis with solar light (low UV-B proportion) in water with natural chromophoric substances is as efficient as or even more efficient than the direct UV-B-induced photolysis. In general, direct photolysis may be slow, because either the pollutants poorly absorb solar light (ethiofencarb, thiobencarb, propiconazole, 4-chloro-2methylphenol) or they are poorly photoreac-tive (acifluorfen, nitrobenzene).

When studies on photolytic degradation were combined with toxicity evaluations of both the educts and products, it has often been shown that the photolytic products were of higher toxicity than the educts. One prominent example is the common fungicide vinclozo-lin, from which three major photodegradation products

Table 2 Half-lives of selected pollutants at 300 nm in pure and natural water (with natural concentrations of chromophoric dissolved compounds), when exposed to solar light

Half-lives r1 =2 (h)

Pure water

Natural water

Propiconazole

85 ± 10

60 ± 10

Nitrobenzene

120 ± 15

100 ± 15

Acifluorfen

133 ± 15

88 ± 10

Ethiofencarb

320 ± 30

40 ± 5

Thiobencarb

320 ± 30

320 ± 30

4-Chloro-2-methylphenol

320 ± 30

18 ± 4

From Vialaton D and Richard C (2002) Phototransformation of aromatic pollutants in solar light: Photolysis versus photosensitized reactions under natural water conditions. Aquatic Sciences 64: 207-215.

From Vialaton D and Richard C (2002) Phototransformation of aromatic pollutants in solar light: Photolysis versus photosensitized reactions under natural water conditions. Aquatic Sciences 64: 207-215.

are significantly more toxic than the parent fungicide itself.

In aquatic, mainly marine systems, photolysis plays also a fundamental role after oil spills. The fate and effects of the oil constituents after a spill are affected by solar radiation through the action of photooxidation and so-called phototoxicity. Photooxidation is the important process in the weathering of oil and produces a variety of oxidized compounds, including aliphatic and aromatic ketones, aldehydes, carboxylic acids, fatty acids, esters, epoxides, sulfoxides, sulfones, phenols, anhydrides, qui-nones, and aliphatic and aromatic alcohols. Some of these compounds contribute to the toxicity toward marine biota observed after an oil spill. Similar to the vinclozolin example, many photolytic products may exhibit elevated toxicities to the marine biota as compared to the educts. However in oil spills, an additional major pathway of toxicity has been found, the phototoxicity. This term comprises that the toxicity of, for instance, certain poly-cyclic aromatic hydrocarbons (PAHs) greatly enhances when the organisms are exposed to both PAHs and sunlight. The mechanisms behind this include absorbance of solar radiation by the PAH which produces a free radical, and this, in turn, reacts with oxygen to produce ROS. Petroleum constituents, particularly anthracene, fluor-anthene, pyrene, and dibenzothiophene, have been shown to be phototoxic to a variety of vertebrate and invertebrate aquatic life in both sediment and water.

Oplan Termites

Oplan Termites

You Might Start Missing Your Termites After Kickin'em Out. After All, They Have Been Your Roommates For Quite A While. Enraged With How The Termites Have Eaten Up Your Antique Furniture? Can't Wait To Have Them Exterminated Completely From The Face Of The Earth? Fret Not. We Will Tell You How To Get Rid Of Them From Your House At Least. If Not From The Face The Earth.

Get My Free Ebook


Post a comment