Evidence for changing the critical level for ammonia.

The current critical level for ammonia (CLE(NH3)) in Europe is set at 8mug NH(3) m(-3) as an annual average concentration. Recent evidence has shown specific effects of ammonia (NH(3)) on plant community composition (a true ecological effect) at much smaller concentrations. The methods used in setting a CLE(NH3) are reviewed, and the available evidence collated, in proposing a new CLE(NH3) for different types of vegetation. For lichens and bryophytes, we propose a new CLE(NH3) of 1 microg NH(3) m(-3) as a long-term (several year) average concentration; for higher plants, there is less evidence, but we propose a CLE(NH3) of 3+/-1 microg NH(3) m(-3) for herbaceous species. There is insufficient evidence to provide a separate CLE(NH3) for forest trees, but the value of 3+/-1 microg NH(3) m(-3) is likely to exceed the empirical critical load for N deposition for most forest ecosystems.

[Surveillance of hepatitis A in the Netherlands 1993-2002]. / Surveillance van hepatitis A in Nederland, 1993-2002.

OBJECTIVE: To survey trends in data on hepatitis A using information from the notification system of the Municipal Medical and Health Services 1993-2002. DESIGN: Retrospective, descriptive. METHOD: Data collected from the notification system of the Dutch Municipal and Medical Services were analyzed. RESULTS: From 1993 to 2002, 64.4%, 6.5% and 11.5% of infections were contracted in the Netherlands, Turkey and Morocco, respectively. Although the absolute number of cases was highest for young people under the age of 16 infected in the Netherlands, incidence rates showed that the children of immigrants infected in Turkey or Morocco were at highest risk, followed by adult immigrants from Turkey and Morocco. In addition, a seasonal trend was observed starting with an increase in the number of notifications of young travellers infected in Turkey and Morocco during their summer holiday, followed by a steep increase in notifications of young people infected in the Netherlands in autumn. This was followed later in the year by a slight increase in notifications of adults who acquired the infection in the Netherlands. However, between 1993-2002 the total number of notifications was halved. This decrease was mainly restricted to infections acquired in the Netherlands. In recent years, fewer outbreaks have been reported in schools, households and families. In 2001, a peak of notifications from the homosexual scene was observed. There was a continued trend in the rise of the mean age of hepatitis-A onset. CONCLUSION: Risk of hepatitis A is highest for the children of immigrants travelling to Turkey or Morocco in the summer months. Secondary cases in the Netherlands are in strong decline, especially in schools and families. However, the almost stable incidence of infections among young people of Turkish or Moroccan extraction stresses the continued importance of immunization of this group before they travel. The continuing trend in the rise of the mean age of hepatitis-A onset deserves attention because of the increasing risk of mortality of the disease amongst older people.

Effects of vapours of chlorpropham and ethofumesate on wild plant species.

Effects of vapours of two herbicides on plantlets of fourteen wild higher plant species and two bryophytes were screened in fumigation experiments using foliar injury, chlorophyll fluorescence and growth as response parameters. After vaporisation of the herbicides for 48 h, concentrations in the chambers reached 77 micrograms m-3 in the chlorpropham treatments and 184 ng m-3 in the ethofumesate treatments. Despite the higher concentrations of the volatile chlorpropham (vapour pressure, VP: 1.3 mP), plants showed no foliar injury, but vapours of this herbicide caused leaf crinkling in the agriophyte Agrostemma githago. The less volatile ethofumesate (VP: 0.56 mP) caused foliar injury in all higher species, with lowest no observed effect concentrations (NOECs) of 75 ng m-3. Chlorpropham affected growth only in Agrostemma, while ethofumesate reduced growth in one third of the higher plant species. Chlorophyll fluorescence proved to be a less suitable response parameter compared to foliar injury and growth. No adverse effects were observed in mosses, probably due to the slow growth and hence small doses of herbicides taken up. The extent of foliar injury due to ethofumesate showed a weak positive relationship to relative growth rates and specific leaf area in the tested higher plant species.

Effects of atmospheric ammonia on vegetation--a review.

Atmospheric ammonia does not only cause acute injuries at vegetation close to the source, but significantly contributes to large scale nitrogen eutrophication and acidification of ecosystems because the amount of sources is high and after conversion to ammonium it can reach remote areas by long-range atmospheric transport. Besides having acute toxic potential, NH(3) and NH(4)(+) (= NH(y)) may disturb vegetation by secondary metabolic changes due to increased NH(y) uptake and assimilation leading to higher susceptibility to abiotic (drought, frost) and biotic (pests) stress. Prevention of damage to natural and semi-natural ecosystems will only be achieved if NH(3) emissions are drastically reduced. In this paper, the current knowledge on NH(y) emission, deposition, and its effects on vegetation and ecosystems are reviewed. Critical levels and critical loads for nitrogen deposition are discussed.

Effects of atmospheric ammonia and ammonium sulphate on vesicular-arbuscular mycorrhizal colonization in three heathland species.

Three heathland species. Arnica montana L., Viola canina L. and Nardus stricta L., were exposed to gaseous ammonia and artificial rain containing ammonium sulphate for 11 wk. Plants infected with Glomus fasciculatum (Thaxter Sensu Gerdemann) Gerd & Trappe grew faster than non-mycorrhizal plants. Ammonia increased the shoot dry weight of both mycorrhizal and non-mycorrhizal V. Canina and mycorrhizal N. stricta. Only mycorrhizal V. canina and non-mycorrhizal N. stricta grew faster when supplied with increasing concentrations of ammonium sulphate. The nitrogen tissue concentration, in all three species, was not influenced by vesicular-arbuscular mycorrhiza (VAM), but increased when plants Wete treated with ammonia. Mycorrhizal and non-mycorrhizal N. stricta and mycorrhizal V. canina had a higher N tissue concentration when supplied with ammonium sulphate. The phosphorus tissue concentration was higher when plants were infected VAM, but tended to be lower in the presence of ammonia or ammonium sulphate. Mycorrhizal plants had higher total amounts of N and P than non-mycorrhizal plants and plants treated with ammonia had higher total amounts of N than non-treated plants. VAM colonization increased in all three species when treated with ammonia but was not affected by exposure to ammonium sulphate. Mycorrhiza decreased the sensitivity of N. stricta to drought, while ammonia decreased the sensitivity to drought for all three species. The effects of additional nitrogen in relation to N/P ratios are discussed with respect to the ecological consequences for these heathland species.

Effects of atmospheric ammonia and ammonium sulphate on Douglas fir (Pseudotsuga menziesii).

Three-year-old Douglas firs (Pseudotsuga menziesii) were fumigated with 180 microg m(-3) NH3 or clean (charcoal-filtered) air. During these fumigations the plants received 15 mm artificial rain weekly, supplemented with 20, 500 or 2500 micromol litre(-1) (NH4)2SO4. Exposure to NH3 and NH4+ for 14 weeks resulted in a change of the nutrient status of the needles. The most remarkable effect was the increase in the N/K ratio, due to both uptake of N and leaching of K. The action of NH3 was stronger than that of NH4+. Both NH3 and (NH4)2SO4 affected the epicuticular wax layer and decreased mycorhiza frequency. Following fumigation and artificial rain treatments, needles were incubated for 8 h in a medium containing 0, 50, 250, 500 and 2500 micromol litre(-1) (NH4)2SO4. Almost no exchange of Ca, Mg and K for NH4+ was found. Therefore this ion exchange probably explains only a minor part of the changes in nutrient status of the whole trees.

Crop loss due to air pollution in The Netherlands.

The extent of yield reduction and economic loss caused by air pollution has been estimated for The Netherlands. Based on available data on direct effects only, each species was designated as sensitive, moderately sensitive or tolerant. On a nationwide scale, only ozone (O3), sulphur dioxide (SO2), and hydrogen fluoride (HF) exceeded effect thresholds. Effects from pollutant combinations were assumed to be additive. Yield reductions were calculated, using 10 exposure-response relationships and concentration data from the Dutch air pollution monitoring network. Changes in air pollution levels result in changes in supply. By multiplying the supply with the current price, the so-called crop volume was calculated. Subsequently, changes in crop volume were converted into economic terms, taking into account demand elasticity. On the basis of these calculations, air pollution in The Netherlands reduces total crop volume by 5%:3.4% by O3, 1.2% by SO2, and 0.4% by HF. The slope of the nonlinear relationship between crop volume reduction and exposure level increases at higher concentrations. In general, air pollution causes relatively little loss to producers, since yield reductions are largely compensated by higher prices. If air pollution in The Netherlands would be reduced to background concentrations, consumers would experience a net gain of Dfl 640 million (US 320 million dollars). Although large amounts of data were attained through literature and our own experience for this study, many assumptions still had to be made to arrive at these conclusions. With the current available knowledge, validation of our results in the field is not yet possible.