petroleum operations, municipal and industrial wastewater, automobile transport,
etc. Hundreds of different PAH compounds have been identified so far; therefore,
routine monitoring primarily focuses on frequently occurring compounds—16
so-called US EPA PAHs or on an extended list of 40 compounds that includes less
common but carcinogenic compounds. The majority of dominant and frequently
found PAHs have molecular weight ranging 120–300 and relatively high hydrophobicity, which allows their enrichment in organic-rich matrices like sediments as well
as bioaccumulation in the organisms and trophic transfer through food webs. Most of
the information on ecotoxicity of individual PAHs is based on studies of prototypical
and broadly occurring compounds like benzo[a]pyrene, anthracene, pyrene. Direct
accumulation in membranes (narcotic toxicity) is one of the common toxicity
mechanisms. Many PAHs easily undergo oxidation upon exposure to UV irradiation, which creates reactive products causing so-called photoactivation
(photoenhanced) toxicity. Reactive oxidized PAHs are also created in the organisms
(bioactivation) during the metabolism, and they cause either direct toxicity to major
biomolecules like proteins or DNA or they indirectly stimulate cellular oxidative
stress. Other important modes of toxicity, shared also with highly hazardous PCDD/
Fs, include activation of aryl hydrocarbon receptor AhR or modulations of metabolic
or hormonal pathways (endocrine disruption). Ecotoxic effects of PAHs have been
studied extensively and include growth and metabolic inhibitions in algae and higher
plants, acute lethality of many aquatic and soil invertebrates (LC50s span across
several orders of magnitude depending on actual molecule and studied species but
may be as low as few μg/g). Highly sensitive are especially fish embryos where
toxicity may manifest at concentrations below μg/L. Other known effects include
mutagenicity and development of neoplasia, immunotoxicity, etc.
27.6.4 Phenols
Phenols are mono- (phenol, cresol, naphthol, xylenol) or poly- (e.g., pyrocatechol,
resorcin, pyrogallol, etc.) hydroxy derivatives of benzene and its alkyl substituents.
They are broadly used in agriculture, pharmacy, or plastic industry; therefore, they
are often released through industrial wastewater. Chlorinated and nitro-phenols are
also used as fungicides or herbicides. Main modes of toxic action of phenols include
basal narcotic toxicity via accumulation to membranes and effects on energy metabolism in mitochondria. In vertebrates they are often toxic to nervous system. For
example, the acute ecotoxicity of phenol to freshwater organisms ranges from few
mg/L (trout, Daphnia magna) up to hundreds mg/L (algae). There are also many
natural polyphenolic compounds, where biological effects like estrogenicity have
been discussed.
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etc. Hundreds of different PAH compounds have been identified so far; therefore,
routine monitoring primarily focuses on frequently occurring compounds—16
so-called US EPA PAHs or on an extended list of 40 compounds that includes less
common but carcinogenic compounds. The majority of dominant and frequently
found PAHs have molecular weight ranging 120–300 and relatively high hydrophobicity, which allows their enrichment in organic-rich matrices like sediments as well
as bioaccumulation in the organisms and trophic transfer through food webs. Most of
the information on ecotoxicity of individual PAHs is based on studies of prototypical
and broadly occurring compounds like benzo[a]pyrene, anthracene, pyrene. Direct
accumulation in membranes (narcotic toxicity) is one of the common toxicity
mechanisms. Many PAHs easily undergo oxidation upon exposure to UV irradiation, which creates reactive products causing so-called photoactivation
(photoenhanced) toxicity. Reactive oxidized PAHs are also created in the organisms
(bioactivation) during the metabolism, and they cause either direct toxicity to major
biomolecules like proteins or DNA or they indirectly stimulate cellular oxidative
stress. Other important modes of toxicity, shared also with highly hazardous PCDD/
Fs, include activation of aryl hydrocarbon receptor AhR or modulations of metabolic
or hormonal pathways (endocrine disruption). Ecotoxic effects of PAHs have been
studied extensively and include growth and metabolic inhibitions in algae and higher
plants, acute lethality of many aquatic and soil invertebrates (LC50s span across
several orders of magnitude depending on actual molecule and studied species but
may be as low as few μg/g). Highly sensitive are especially fish embryos where
toxicity may manifest at concentrations below μg/L. Other known effects include
mutagenicity and development of neoplasia, immunotoxicity, etc.
27.6.4 Phenols
Phenols are mono- (phenol, cresol, naphthol, xylenol) or poly- (e.g., pyrocatechol,
resorcin, pyrogallol, etc.) hydroxy derivatives of benzene and its alkyl substituents.
They are broadly used in agriculture, pharmacy, or plastic industry; therefore, they
are often released through industrial wastewater. Chlorinated and nitro-phenols are
also used as fungicides or herbicides. Main modes of toxic action of phenols include
basal narcotic toxicity via accumulation to membranes and effects on energy metabolism in mitochondria. In vertebrates they are often toxic to nervous system. For
example, the acute ecotoxicity of phenol to freshwater organisms ranges from few
mg/L (trout, Daphnia magna) up to hundreds mg/L (algae). There are also many
natural polyphenolic compounds, where biological effects like estrogenicity have
been discussed.
560
L. Bláha and J. Hofman