J.N.B. Bell

Effect of air pollution on peri-urban agriculture: a case study

Peri-urban agriculture is vital for the urban populations of many developing countries. Increases in both industrialization and urbanization, and associated air pollution threaten urban food production and its quality. Six hour mean concentrations were monitored for SO(2), NO(2) and O(3) and plant responses were measured in terms of physiological characteristics, pigment, biomass and yield. Parameter reductions in mung bean (Vigna radiata), palak (Beta vulgaris), wheat (Triticum aestivum) and mustard (Brassica compestris) grown within the urban fringes of Varanasi, India correlated directly with the gaseous pollutants levels. The magnitude of response involved all three gaseous pollutants at peri-urban sites; O(3) had more influence at a rural site. The study concluded that air pollution in Varanasi could negatively influence crop yield.

Competitive effects of potassium and ammonium on caesium uptake kinetics in wheat

Caesium (Cs) uptake by roots of winter wheat is known to obey Michaelis-Menten kinetics. As a result, the solution-to-root transfer factor for radiocaesium is depressed in a non-linear fashion by increasing the concentration of stable caesium (133Cs) in the external solution. It is likely that 133Cs concentrations in the environment are insufficient to result in this effect being observed. However, any environmentally abundant ion which demonstrates a general physiological equivalence with the Cs+ ion may exert a similar effect on the soil-to-plant transfer factor for radiocaesium. The K+ and NH4+ ions are members of the same homologous series to which the Cs+ ion belongs. A mechanistic scheme of root uptake competition between these ions is proposed which envisages Cs uptake as a reaction which may be competitively inhibited by any ‘analogous’ ion. A series of equations is presented describing this inhibition of Cs uptake in terms of its effect on the solution-to-root transfer factor for radiocaesium. Experimental data gathered in the cases of the inhibition of radiocaesium uptake by the K+ and NH4+ ions show a generally good agreement with the proposed theoretical relationships over the concentrations ranges of K+ and NH4+ (0–10 μM) examined.

Effects of sulphur pollutants on the growth of Sphagnum species

Abstract Sphagnum species, once dominant in the blanket bog vegetation of the southern Pennines, have largely disappeared since the Industrial Revolution. Laboratory studies suggest that the growth of a number of Sphagnum species is sensitive to sulphur pollutants (− HSO3, −− SO4, SO2) within the range of concentrations found in Great Britain today. The species differ in their response to the pollutants; 0·5 mM −HSO3 eventually proved lethal to the most sensitive species but reduced the growth rate of the most resistant, S. recurvum, by only 35%. These results are discussed in relation to vegetation changes in the southern Pennines and north Cheshire.

Air pollution and its impacts on wheat yield in the Pakistan Punjab

A study using open-top chambers ventilated with ambient or charcoal-filtered air in the vicinity of Lahore, Pakistan, has demonstrated a reduction of 46.7% and 34.8% in the grain yield for two cultivars of winter wheat (Triticum aestivum L.). The 6-h daily mean O(3) concentrations were 25-45 nl litre(-1) and on the basis of experience in North America and Europe, reductions in yield in the present study are substantially greater than might be predicted. The reasons for this discrepancy are discussed, together with implications for the suitability of a simple, relatively cheap, open-top chamber system for developing-country studies on the effects of air pollution on crops.

Effects of air pollution on rice yield in the Pakistan Punjab

A study using open-top chambers ventilated with ambient or charcoal filtered air in the vicinity of Lahore, Pakistan demonstrated reductions of 42% and 37% in the grain yield of two cultivars of rice (Oryza sativa L.). This yield reduction was primarily due to the reduction in mean panicle number per plant, although significant effects of filtration on 1000 grain weight and the number of filled grains per panicle were also detected. The 6-h daily mean O(3) concentrations were only 10-20 nl litre(-1) during the monsoon season, but increased to 30-55 nl litre(-1) later in the growing season, while the mean NO(2) concentration during the experiment was 12 nl litre(-1). On the basis of experience in North America and Japan, the reductions in yield in the present study are substantially greater than might be predicted. The reasons for this discrepancy are discussed, together with the implications for effects on rice yield in other regions of south and south-east Asia.

Radiocaesium uptake and translocation in wheat with reference to the transfer factor concept and ion competition effects

A theoretical scheme is presented which considers the uptake of radiocaesium by roots of wheat and its subsequent translocation to above ground tissues. This is tested experimentally against data derived for actively growing plants in the presence of increasing concentrations of stable caesium (133Cs), potassium (K) and ammonium (NH4). Transfer functions for 137Cs are defined in the presence of each of these ions. Mean transfer factors derived for roots over the ion concentration ranges examined were approximately one order of magnitude greater than those for shoots and transfer functions in all cases were distinctly non-linear. Experimental data adhered closely to the model in all instances except that of K+ at an external concentration greater than 20 μM. This anomaly is identified as an ion-specific effect with important radioecological implications. The uses and limitations of the soil-to-plant transfer concept and simple mechanistic models such as that presented here are discussed with reference to the problem of modelling the movement of radioactive substances within the environment.

Vegetation—The missing sink in the global cycle of carbonyl sulphide (COS)

Abstract It has been suggested that carbonyl sulphide (COS) represents the major form of atmospheric sulphur on a global scale, and that oxidation of COS in the stratosphere may affect the climate by influencing the formation of the sulphate aerosol layer. Despite the apparent importance of COS to the global environment, considerable uncertainties remain as to its pathways in the atmosphere, particularly in regard to its sinks. In this paper, we review evidence from studies on deposition of COS to plants which provides preliminary confirmation of the hypothesis that uptake of COS by vegetation may be the major global sink for the gas, accounting for 2–5 Tg y−1 (Tg = 1012g). In contrast, uptake by soil can account for a maximum of only 0.04 Tg y−1. Confirmation of these estimates must await measurements of COS flux to vegetation representative of the major biomes of the world.

Calculating human exposure to endocrine disrupting pesticides via agricultural and non-agricultural exposure routes.

Endocrine Disrupting Chemicals (EDCs) are of increasing concern because of their potential impacts on the environment, wildlife and human health. Pesticides and some pesticide metabolites are an important group of EDC, and exposure to them is a poorly quantified source of human and environmental exposure to such chemicals generally. Models for estimating human exposure to Endocrine Disrupting (ED) pesticides are an important risk management tool. Probabilistic models are now being used in addition to deterministic ones in all areas of risk assessment. These can provide more realistic exposure estimates, because they are better able to deal with variation and uncertainty more effectively and better inform risk management decisions. Deterministic models are still used and are of great value where exposure data are scarce. Models or groups of models that provide holistic human ED pesticide exposure estimates are required if the risk posed to humans by ED pesticides is to be better assessed. Much more research is needed to quantify different exposure routes such as exposure from agricultural spray drift and the medical use of pesticides to develop such models. Most available probabilistic models of human exposure were developed in the USA and require modification for use elsewhere. In particular, datasets equivalent to those used to create and apply the American models are required. This paper examines the known routes of human pesticide exposure with particular reference to ED pesticides and their quantification as unlike pesticides generally, many ED pesticides are harmful at very low doses, especially if exposure occurs during sensitive stages of development, producing effects that may not manifest for many years or that affect descendants via epigenetic changes. It also summarises available deterministic and probabilistic models commonly used to calculate human exposure. The main requirement if such models are to be used in the UK is more quantitative data on the sources and pathways of human ED pesticide exposure.

The Kinetics of Caesium absorption by roots of winter wheat and the possible consequences for the derivation of soil-to-plant transfer factors for radiocaesium

Abstract Caesium (Cs) uptake in roots of winter wheat was found to follow a dual pattern similar to that established for potassium uptake in barley roots. This suggests the operation of two discrete uptake systems for Cs, as for potassium. The ‘System 1’ (low concentration) uptake mechanism for caesium, however, can be resolved into two hyperbolic components which both obey Michaelis-Menten kinetics. The Michaelis-Menten equation was used to derive a function which describes the variation in solution-to-root transfer factor for any element for which the appropriate root uptake constants (K m and V max ) can be determined. This function successfully described available data for root uptake of caesium and potassium, predicting that the solution-to-root transfer factor decreases in relation to an increase in the substrate concentration of each respective element. At substrate concentrations equivalent to carrier-free radiocaesium concentrations, however, the solution-to-root transfer factor predicted by the function and by empirical data suggests that the relationship between root uptake and solution concentration of caesium is linear. These findings are discussed in relation to the comparative physiology of caesium and potassium uptake by plant roots and with respect to the application of the soil-to-plant transfer factor concept to radioecological studies.

EFFECT OF OZONE ON RADISH AND TURNIP UNDER EGYPTIAN FIELD CONDITIONS

EDU was used to assess the impact of ozone on the growth and yield of local varieties of radish (Raphanus sativus L.) and turnip (Brassica rapa L.) at two sites in northern Egypt. At a suburban site, in Alexandria, the growth of radish was significantly increased by application of the anti-ozonant N-[2-(2-oxo-l-imidazolidinyl) ethyl]-N′phenylurea (EDU) but turnip was unaffected. At a rural site, Abbis, 35 km south of Alexandria, the increase in growth of radish caused by EDU was higher than at Alexandria, and a significant increase in the growth of turnip was also found. These effects were consistent with the higher oxidant concentrations measured at Abbis compared with Alexandria. A controlled experiment involving ozone or filtered air treatments in open-top chambers demonstrated protective effects of ED U against ozone of a similar size found in the field, and that ED U had no significant effect on these species in the absence of ozone. This provides confidence that the effects of EDU in the field in Egypt can be ascribed to O3. The implications of the results for Egyptian agriculture are considered.