Phytotoxic pollutants

Leuenberger C, Czuczwa J, Tremp J, et al. 1988. Nitrated phenols in rain Atmospheric occurrence of phytotoxic pollutants. Chemosphere 17 511-515. 

By far, ozone is the most important of the phytotoxic pollutants. A large volume of literature has been published dealing with the influence of 03 on higher plants. Highlights of the experimental results include the following ... 

Monaci et al. (1997) performed a lichen-biomonitoring study in Siena by means of two different methods. The pattern of air quality in the study area was examined on the basis of the in situ frequency of different species of epiphytic lichens, i.e. using their species-specific sensitivity to the complex mixture of phytotoxic pollutants in the urban environment. The distribution of trace elements was evaluated quantitatively by an analysis of thalli of a tolerant species, P. caperata, known to be a reliable bioaccumulator of persistent atmospheric pollutants. The values obtained for Al, Ba, Cr, Cu, Fe, Pb and S were significantly higher in Sienese lichens over and above controls. Traffic was found to be the major source of atmospheric pollution. The pattern of trace-elemental deposition did not always coincide with air quality. lAP values were found to reflect essentially the emission of gaseous phytotoxic pollutants in the urban environment. 

Croisetiere L, Rouillon R, Carpentier R. A simple mediatorless amperometric method using the cyanobacterium Synechococcus leopoliensis for the detection of phytotoxic pollutants. Appl Microbiol... 

Frank H, H Scholl, D Renschen, B Rether, A Laouedj, Y Norokorpi (1994) Haloacetic acids, phytotoxic secondary air pollutants. Environ Sci Pollut Res 1 4-14. 

Although ozone and PAN are considered the two primary phytotoxic oxidants in the photochemical complex, the specific response of plants to many simulated atmospheres suggests the existence of other phytotoxic oxidants. The symptoms associated with many of these reactant mixtures are closely related to those caused by ozone and PAN. In some tests, the mixtures used would not have produced either ozone or PAN. In other cases, leaf age or the pattern of injury on sensitive test plants suggested one or more pollutants other than ozone or PAN. Field injury symptoms often resemble those reported for ozone or PAN, but the response pattern is sufficiently different that accurate diagnosis is difficult. Brennan et al. correlated development of oxidant symptoms with aldehyde concentrations in New Jersey and suggested that aldehyde may be a major phytotoxic component of the photochemical-oxidant complex. The symptoms were probably not responses to the aldehyde, but rather to some compound or group of compounds present under the same conditions as the aldehyde. ... 

Oxidant air pollutants exist as parts of a complex mixture of gases, many of which may be phytotoxic. However, expect for ambient-air studies and simulated photochemical-oxidant studies, little research was done with pollutant combinations until the classic work of Menser and Heggestad in 1966. It is of interest that Thomas et suggested that sulfur dioxide might lessen the effect of oxidants in causing foliar injury to pinto bean. Middleton et working with ratios of sulfur... 

Most research workers are now convinced that pollution abatement will have little impact on overall pollution concentrations until dean energy forms are developed and in widespread use. Because phytotoxic concentrations of ozone and other oxidants are inevitable for the foreseeable future, researchers are seriously considering other means of protecting plants from Injurious effects of oxidants. 

Acute Inhibition of Apparent Photosynthesis by Phytotoxic Air Pollutants... 

Sublethal plant exposures to a number of phytotoxic air pollutants can cause the reversible suppression of one of life s most basic processes— photosynthesis. The possibility of plant growth suppression by atmospheric pollution is a concern of many people. We need to know if subnecrotic pollutant exposures that may occur in ambient air can repress photosynthesis rates sufficiently to cause significant retardation of plant growth. Some insight into the capability for short-term exposures to HF, CI2, O3, S029 NO2 and NO— applied singly and as dual pollutant mixtures— to suppress apparent photosynthesis rates of several important crop species is presented here. 

Phytotoxic atmospheric pollutants have been rated by plant... 

Sulfur dioxide (SO2) is regarded as the most important phytotoxic air pollutant emitted from industrial (point) sources. 

Information presently available will allow only a first approximation to be made into the significance of air pollution on plant growth. To complicate an evaluation, very little is known about the impact of various pollutant combinations that might interact to determine the phytotoxicity of the mixtures. Current knowledge about the inhibitory effects of major air pollutants on apparent photosynthetic rates in plants is described below. The discussion includes observed plant responses to simple dual combinations of the pollutants. 

At least six major phytotoxic air pollutants have been shown to reversibly inhibit apparent photosynthetic rates in plants (1 - ). Studies indicate that these phytotoxicants ranked in the following order according to the relative amount of inhibition effected after several hours of exposure to equal pollutant concentrations HF>Cl2-03>S02>N02>N0. A summary of the experimental results which compares measured depressions in CO2 uptake rates of barley and oat canopies after 2-hr pollutant exposures in environmental chambers appears in Figure Typical inhibition and recovery rate curves for exposures that reduced CO2 absorption rates by 20 percent at the end of the 2-hr fumigations are also shown. Similar data have been obtained for alfalfa, another important crop species which was cultured and exposed under identical conditions In contrast, equivalent... 

Another important phytotoxic atmospheric pollutant that has been studied with respect to its inhibitory effects on plant photosynthesis is peroxyacetyl nitrate (PAN). This phytotoxicant applied for 30 min at 1 ppm depressed the incorporation of 1 C02 into intact pinto bean leaves, but only after visible tissue injury started to develop (20). From companion studies on isolated chloroplasts, it was concluded that PAN-induced inhibition was probably associated with the carboxylating reaction or the chloroplast light-energy conversion system leading to assimilative power. The inhibition appeared to result in a quantitative reduction (but not a qualitative change) in the early products of photosynthesis. 

In real atmospheres a wide array of pollutant combinations may occur. Plant responses described here represent only experimental combinations of major pollutants shown to inhibit CO2 absorption rates. Effects of other important phytotoxic atmospheric pollutants such as ethylene should also be examined along with more complex mixtures. Information regarding the responses of a wider range of plants subjected to varied environmental conditions would further aid in clarifying the problem. 

Of the phytotoxic air pollutants and mixtures tested, O3 or combinations of SO2+NO2 are most likely to occur in ambient atmospheres in sufficiently high concentrations to acutely depress apparent photosynthesis. Ambient HP concentrations of the magnitudes which inhibited CO2 uptake rates in an acute, reversible manner would be rare. Studies into longer-term exposures (several days or weeks) to HP concentrations in the low ppb range have suggested that reduced photosynthesis under these conditions correlated with the amount of necrosis that developed (, ). 

Lewis, M.A. (1995) Use of freshwater plants for phytotoxicity testing a review, Environmental Pollution 87 (3), 319-336. 

Oxidation/hydroxylation of aromatic compounds by OH and HOONO is expected to enhance their degradation rate and hence decrease their lifetime on particulate matter, which in the case of pollutants is beneficial from the point of view of human health. Oxidation of PAHs could also lead to the production of photosensitizers such as quinones and aromatic carbonyls [10, 40, 41]. These compounds, if present in the gas phase, are also able to form aggregates and are therefore involved in the formation of secondary organic aerosol [42]. In contrast, nitration induced by OH + N02 or HOONO could lead to highly mutagenic nitro-PAHs [43] or phytotoxic nitrophenols [44, 45], in which case the health and environmental impact of the reaction intermediates is not negligible and is sometimes higher than that of the parent molecules. 

Most metals are phytotoxic when present in soils to excess, even those that are essential plant micronutrients. There are various places in the world where, either naturally or through anthropogenic pollution, the soils contain elevated concentrations of metals that will kill most normal plants. These places are rarely devoid of plant life, however, even though the range of species present on the contaminated site will frequently be much less than in uncontaminated but otherwise similar sites in the immediate vicinity. When those species are investigated it is normally found that the populations inhabiting these sites have evolved tolerance to the metals present in the soils, and that populations of the same species from uncontaminated areas show normal levels of susceptibility to the metal toxicity. Since many of the sites where tolerant plants have been found have been contaminated in the very recent past (sometimes as little as 30 years before), this indicates very rapid evolution of an adaptation. This phenomenon has proved to be one of the clearest examples of microevolution , and has excited much interest and research on a number of fronts. There have been several reviews on this topic in recent years (Baker, 1987 Macnair, 1987 Shaw, 1990). In this chapter we will concentrate on these topics in which research is most active, and where we believe that further research effort is most needed. 

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