Accumulation of atmospheric deposition of As, Cd and Pb by bush bean plants.

Bush bean (Phaseolus vulgaris) was exposed to atmospheric deposition of As, Cd and Pb in a polluted and a reference area. The atmospheric deposition of these elements was significantly related to the concentrations in leaves, stems and pods at green harvest. Surprisingly there was also a clear relation for As and Pb in the seeds at dry harvest, even though these seeds were covered by the husks. Root uptake of accumulated atmospheric deposits was not likely in such a short term experiment, as confirmed by the fact that soil pore water analysis did not reveal significant differences in trace element concentrations in the different exposure areas. For biomonitoring purposes, the leaves of bush bean are the most suitable, but also washed or unwashed pods can be used. This means that the obtained relationships are suitable to estimate the transfer of airborne trace elements in the food chain via bush bean.

Potential impact of fertilization practices on human dietary intake of dioxins in Belgium.

Dioxins can enter the food chain at any stage, including crop fertilization. Therefore, we developed a simple method for estimating the introduction of dioxins in the food chain according to various fertilization practices. Using dioxin's contamination data taken from the literature, we estimated that fertilization accounts for approximately 20% of the dioxin inputs on agricultural soils at country scale. For the estimations at the field scale, 6 fertilization scenarios were considered: sludge, compost, digestate, manure, mineral fertilizers, and a common fertilization scenario that corresponds to an average situation in Belgium and combines mineral and organic fertilizers. According to our first estimations, mineral fertilizers, common fertilization practices or manure bring less than 1 ng TEQ/m² while atmospheric deposition or digestate bring between 1 and 3 ng TEQ/m² and sludge or compost bring more than 3 ng TEQ/m². The use of solid fertilizers could potentially increase the dioxin levels in the 30 cm agricultural soil layer by 0 to ~1.5% per year (up to ~9% for the 5 cm thick surface layer). For animals, the increase in dioxin ingestion linked to the fertilization practices is lower than 1% for most scenarios with the exception of the compost scenario. Increases in human dietary intake of dioxin are estimated to be lower than 1% for conventional rearing methods (i.e. grazing animals are reared outdoor while pigs and poultry are reared indoor). Spraying liquid fertilizers on meadows and fodder crops, even if very limited in practice, deserves much more attention because this application method could theoretically lead to higher dioxin's intake by livestock (from 6 to ~300%). Considering an average half-life of dioxins in soils of 13 years, it appears that the risks of accumulation in soils and in the food chain are negligible for the various fertilization scenarios.

A comparison of two stomatal conductance models for ozone flux modelling using data from two Brassica species.

In this study we tested and compared a multiplicative stomatal model and a coupled semi-empirical stomatal-photosynthesis model in their ability to predict stomatal conductance to ozone (gst) using leaf-level data from oilseed rape (Brassica napus L.) and broccoli (Brassica oleracea L. var. italica Plenck). For oilseed rape, the multiplicative model and the coupled model were able to explain 72% and 73% of the observed gst variance, respectively. For broccoli, the models were able to explain 53% and 51% of the observed gst variance, respectively. These results support the coupled semi-empirical stomatal-photosynthesis model as a valid alternative to the multiplicative stomatal model for O3 flux modelling, in terms of predictive performance.

Chlorophyll a fluorescence imaging of ozone-stressed Brassica napus L. plants differing in glucosinolate concentrations.

Brassicaceae are characterised by glucosinolates (GS), which appear to be involved not only in biotic but also in abiotic stress responses of plants. We investigated the effect of O (3) stress on leaf GS concentrations in two lines of BRASSICA NAPUS L., differing in GS content. Ozone fumigation decreased GS concentrations in leaves of B. NAPUS of one line. In control conditions, chlorophyll content, rates of saturating photosynthesis, and quantum yield of photosystem 2 differed between the two BRASSICA lines, but differences were smaller in O (3)-stress conditions, suggesting that the relationship between leaf GS concentration and sensitivity to abiotic stress merits further research. In agreement with other ecophysiological measurements, chlorophyll fluorescence imaging clearly distinguished both lines and in some cases also treatments. A method for analysis of fluorescence images accounting for the two-dimensional leaf heterogeneity is presented.

Phenological weighting of ozone exposures in the calculation of critical levels for wheat, bean and plantain.

This paper presents phenological weighting factors to be applied to AOT40 (accumulated ozone exposure above a threshold of 40 nl l(-1)) ozone exposure-response relationships for crops at different growth stages. The quantification of such factors represents a step-forward in the derivation of Level II critical levels for ozone. The weighting factors presented are derived from published literature on the sensitivity of wheat (Triticum aestivum), bean (Phaseolus vulgaris) and plantain (Plantago major) to ozone at different growth stages. Weighting functions were calculated using either multiple linear regression or the reciprocal residual mean square (RMS(-1)). The resulting weights were transformed into multiplication factors to be applied to the monthly AOT40 during the 3-month assessment period of critical level exceedance. Interspecific differences were too large to allow for the development of a unified weighting function for the three species considered. For wheat grain yield, the derived multiplication factors varied by almost four-fold (0.40, 1.06, 1.54), while those for bean pod yield varied by only about 25% (0.85, 1.01, 1.14). The available data for plantain were restricted to short-term studies conducted under controlled conditions. These data were not suitable for the derivation of weighting factors comparable to those derived for bean and wheat. Based on known differences in wheat development and phenology across Europe, the need for a geographic differentiation of the time period for the calculation of the critical level exceedances is also discussed and examples provided of the adoption of the derived weightings in the mapping of critical level exceedances. Differences between critical level exceedance maps using weighted and unweighted AOT40 calculations are discussed.

Effects of air filtration on spring wheat grown in open-top field chambers at a rural site. I. Effects on growth, yield and dry matter partitioning.

Spring wheat, Triticum aestivum, was grown in open-top field chambers and exposed during the whole life cycle to filtered and non-filtered ambient air. The relatively low ambient pollution level did affect plant growth but had no effect on the overall grain yield of the two spring wheat cultivars Echo (1987) and Pelican (1988). A reduced root growth was found in both years which could be attributed mainly to the deposition of NO2 and SO2. Effects on crop development most likely due to ozone were limited to the 1987 growing season during which the ambient ozone concentrations were enhanced compared to 1988. This resulted in a slightly increased grain harvest index, a reduced 1000-grain weight, straw yield and a greater reduction in root growth. Visible damage resembling ozone injury appeared both years during seedling growth.

Effects of air filtration on spring wheat grown in open-top field chambers at a rural site. II. Effects on mineral partitioning, sulphur and nitrogen metabolism and on grain quality.

In 1988 the effect of ambient levels of air pollutants on the nutrients status and grain quality of spring wheat (Triticum aestivum cv. Pelican) was investigated by comparing plants grown in open-top chambers (OTC) ventilated with ambient air (NF treatments) and charcoal-filtered air (CF treatments) at a rural site (Tervuren, Belgium). Spring wheat cultivated in NF OTC showed only minor differences in the P, K, Ca, Mg, Mn and Na concentrations of the different plant parts at final harvest, as well as organic and inorganic S fractions, compared to those of the plants grown in CF air. The plants' total P content was reduced, as well as the P and K concentration of the flour. The total S concentration of the flour was increased by 4%. Effects on N concentrations and grain quality were much more pronounced. At final harvest the N concentrations of straw and flour of the NF air treated plants were much higher compared to CF air. However, the N content of the aerial biomass and the grain N yield were not significantly affected, implying a reduction of other structual compounds. Nitrogen harvest index (NHI) and the ratio of NHI over grain harvest index (GHI), indicated a significant reduction of N translocation from the above-ground biomass to the grain. Changes in the N status and partitioning of spring wheat had an effect on the baking quality of wheat flour. Several parameters that are commonly used as an indication of baking quality have been significantly increased in the NF treatment: total protein concentration, Zeleny value, dry and wet gluten concentration. A slightly increased Hagberg value indicated a reduced alpha-amylase activity. The possibility of foliar N uptake as an additional N source, especially after anthesis and implications of increased protein production instead of carbohydrate synthesis are discussed.