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PubMed2002

N uptake and distribution in crops: an agronomical and ecophysiological perspective.

The rate of N uptake of crops is highly variable during crop development and between years and sites. However, under ample soil N availability, crop N accumulation is highly related to crop growth rate and to biomass accumulation. Critical N concentration has been defined as the minimum N concentration which allows maximum growth rate. Critical N concentration declines during crop growth. The relationship between critical N concentration and biomass accumulation over the growth period of a crop is broadly similar within major C(3) and C(4) cultivated species. Therefore, the critical N concentration concept is widely used in agronomy as the basis of the diagnosis of crop N status, and allows discrimination between situations of sub-optimal and supra-optimal N supply. The relationship between N and biomass accumulation in crops, relies on the interregulation of multiple crop physiological processes. Among these processes, N uptake, crop C assimilation and thus growth rate, and C and N allocation between organs and between plants, play a particular role. Under sub-optimal N supply, N uptake of the crop depends on soil mineral N availability and distribution, and on root distribution. Under ample N supply, N uptake largely depends on growth rate via internal plant regulation. Carbon assimilation of the crop is related to crop N through the distribution of N between mature leaves with consequences for leaf and canopy photosynthesis. However, although less commonly emphasized, carbon assimilation of the crop also depends on crop N through leaf area development. Therefore, crop growth rate fundamentally relies on the balance of N allocation between growing and mature leaves. Nitrogen uptake and distribution also depends on C allocation between organs and N composition of these organs. Within shoots, allocation of C to stems generally increases in relation to C allocation to the leaves over the crop growth period. Allocation of C and N between shoots and roots also changes to a large extent in relation to soil N and/or crop N. These alterations in C and N allocation between plant organs have implications, together with soil availability and carbon assimilation, on N uptake and distribution in crops. Therefore, N uptake and distribution in plants and crops involves many aspects of growth and development. Regulation of nitrogen assimilation needs to be considered in the context of these interregulatory processes.

Agriculture↗
PubMed1998

Release of heavy metals from European and Asian porcelain dinnerware.

Samples of porcelain dinnerware manufactured in five European and three Asian countries before the mid-1970s and subsequently brought into the US were subjected to acid leaching tests to investigate the release of heavy metals. Forty-six dishes decorated with decals or hand painted designs applied over the glaze were examined. Included in the selection were dishes from major manufacturers of fine dinnerware (Haviland Limoges, Rosenthal, Noritake) as well as samples from lesser-known or unidentified factories. During 24-h tests with 4% acetic acid, half of the samples (23 dishes) released lead in concentrations exceeding the US Food and Drug Administration (FDA) allowable maximum of 3.0 micrograms/ml and another 17 dishes released lead in concentrations ranging from 0.1 to 2.9 micrograms/ml. Five dishes released cadmium, but only one value exceeded the FDA limit of 0.5 microgram/ml. Zinc, cobalt, copper and chromium were also released by some of the dishes. None of the acetic acid solutions contained measurable concentrations of nickel although this metal, as well as those named above, could be extracted from some samples with 6 M nitric acid. The FDA has not established dinnerware extraction limits for any metals except lead and cadmium. All overglaze-decorated dishes imported into the US before the mid-1970s should be tested for lead release before they are used in the preparation, serving, or storage of food.

Acetic Acid↗
PubMed2005

Toxicity of atrazine to the juvenile hard clam, Mercenaria mercenaria.

The herbicide atrazine is one of the most heavily used pesticides in the United States. The effects of atrazine on the clam Mercenaria mercenaria were evaluated in aqueous and sediment laboratory assays. Juvenile clams of approximately 1mm in size were used for all experiments. An acute aqueous bio-assay was used to determine the 96-h LC(50) for the juvenile clams. A chronic aqueous bioassay was conducted at lower atrazine concentrations over a 10-day exposure period to examine both lethal and sublethal (dry mass, shell size, and condition index) endpoints. A chronic sediment bioassay examined mortality and sublethal endpoints in a 10-day exposure. The acute 96-h LC(50) was 5608 microg/L with 95% confidence intervals ranging from 5003 to 6287 microg/L. Results of the chronic aqueous assay indicated both lethal and sublethal (reduced shell size) effects at high atrazine concentrations. In the 10-day chronic aqueous assay, the no observable effect concentration was 500 microg/L, the lowest observable effect concentration was 1000 microg/L, and the maximum allowable toxicant concentration (MATC) was 707 microg/L. There were no significant effects of atrazine in the chronic sediment exposure. Safe concentrations for the aqueous experiments were estimated by applying an uncertainty factor of 10 to the calculated MATC values. While there were adverse effects of atrazine at high concentrations, these results suggest that atrazine is not directly toxic to M. mercenaria at environmentally relevant concentrations.

Animals↗
PubMedDate not supplied

Impact of air pollution by lead on the heme biosynthetic pathway in school-age children.

Blood-lead level (Pb-B), erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity, free erythrocyte porphyrin (FEP) concentration, delta-aminolevulinic acid concentration in urine (ALAU), hematocrit value, and hemoglobin concentration were compared for groups of children 10-13 years old from areas differently polluted by lead (rural area and lead smelter area). The biological responses of the children were also compared with those observed in adults similarly exposed to lead (Pb-B: 10-40 mug/100 ml). Compared with the rural children, children living less than 1 km from the smelter exhibited a significant increase of Pb-B and FEP, a significant inhibition of ALAD, and a slight positive correlation of ALAU with Pb-B; however, they showed no biological signs of anemia. In children living approximately 1.5 km from the smelter, there was still a significant increase of Pb-B and a concomitant inhibition of ALAD, but no change in FEP concentration. Comparison of the dose-response curves between Pb-B and FEP in adult males, adult females, and children indicates that the sensitivity to lead is in the order of children larger than or equal to women greater than men. Based on the FEP response, it is proposed that 25 mug Pb/100 ml blood be regarded as the maximum biologically allowable concentration of lead in blood of school-age children.

Adolescent↗
PubMed1996

[Urban air pollution by carcinogenic N-nitrosamines].

Moscow is used as an example to discuss the problem of urban atmospheric pollution by carcinogenic N-nitrosamines. An analytical method is proposed, which is based on the use of a Russian gas chromatograph compatible with a chemiluminescence detector, that is a TEA thermal energy analyzer (USA) having some modifications to reduce the time of analysis and loss during sample pretreatment. The minimal detected concentration is 3 ng/m3 for 2-hour sampling. The method identifies and quantifies 7 volatile N-nitrosamines: N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine, N-nitrosodibutylamine, N-nitrosodipropylamine, N-nitrosopiperidine, N-nitrosopyrrolidine, N-nitrosomorpholine. The pollution of the Moscow air was evaluated in the center of Moscow (30-60 ng/m3 for NDMA), in the industrial emission area (as high as several hundred ng/m3, and in the heavy traffic area (100 ng/m3 or more). It is proposed to study the working area for rubber and tire industries, to establish nitrosamine tolerances for these industries and maximum allowable discharge concentrations in the urban air and to monitor these parameters.

Air Pollutants↗
PubMedDate not supplied

[The hygienic assessment of atmospheric pollution by xylene isomers].

The biological action of xylol isomers as ambient air pollutants was investigated. The maximum single allowable concentrations of orthoxylol (0.3 mg/m3), methaxylol (0.24 mg/m3), papaxylol (0.27 mg/m3) were determined by measuring the odour thresholds of the substances in 122 volunteers. The average daily allowable concentrations of the xylol isomers were found to be 0.4, 0.16, and 0.96 mg/m3, respectively.

Adolescent↗
PubMed1996

[Present-day health policy in the area of chemical safety].

The article deals with priority spheres of anti-chemical protection of workers and general population in up-to-date conditions. The authors suggest and discuss new definition for a term "maximal allowable concentration".

Hazardous Substances↗
PubMed2002

[In vitro resistance acquisition in Mycoplasma gallisepticum against ofloxacin, tylosin and spectinomycin].

To clarify a mechanism of acquired resistance of two Mycoplasma gallisepticum (MG) strains against ofloxacin (OFLX) along with tylosin (TS) and spectinomycin (SPCM) as the controls, in vitro resistance acquisition test was carried out for 10 subcultures of each strain with increasing the amount of antimicrobials, and maximum growth allowance concentrations (MAC) in 10th and primary subcultures were compared. Acquisition of resistance in the strains against OFLX was moderate and MAC of the 10th subculture increased twice for one strain and 16 times for another one as compared to that of their primary subcultures. Acquisition of resistance in the strains against TS was also moderate and MAC of the 10th subculture increased 8 times for both strains as compared to that of the primary subcultures. Acquisition of resistance against SPCM was quite different between the strains. Namely the MAC of one strain increased 512 times, while another one did not acquire any resistance.

Anti-Bacterial Agents↗
PubMed2005

The role of sediments in the assessment of ecological quality of European river bodies.

Member States of the EU are presently involved in the enforcement of the Directive of the Council and European Parliament 2000/60/CE, the so-called Water Framework Directive (WFD), establishing a frame for the common water policy of the Union. A major objective of the WFD is to reach within 2015 a good ecological status for all relevant surface water bodies of the Union territory. The assessment of the ecological status must be supported by the assessment of both the hydromorphological conditions of the water and its chemical status as represented by basic chemical parameters such as temperature, pH, oxygen balance and nutrients, and the presence or absence (vs environmental quality standards or natural background concentration) of specific synthetic and non-synthetic micropollutants. According to this approach, the assessment of the presence in any phase (water, sediments and biota) constituting the water body of micropollutants at concentrations below the environmental standards will guarantee the protection from toxic and ecotoxic effects on humans, animal and vegetal communities associated with the water body. In this context, the state of the art in Italy as compared to that in some non-EU states, particularly in Armenia, is discussed.

Animals↗