Stephan Köppchen

Continuous Turnover of Carotenes and Chlorophyll a in Mature Leaves of Arabidopsis Revealed by 14CO2 Pulse-Chase Labeling

Carotenoid turnover was investigated in mature leaves of Arabidopsis (Arabidopsis thaliana) by 14CO2 pulse-chase labeling under control-light (CL; 130 μmol photons m−2 s−1) and high-light (HL; 1,000 μmol photons m−2 s−1) conditions. Following a 30-min 14CO2 administration, photosynthetically fixed 14C was quickly incorporated in β-carotene (β-C) and chlorophyll a (Chl a) in all samples during a chase of up to 10 h. In contrast, 14C was not detected in Chl b and xanthophylls, even when steady-state amounts of the xanthophyll-cycle pigments and lutein increased markedly, presumably by de novo synthesis, in CL-grown plants under HL. Different light conditions during the chase did not affect the 14C fractions incorporated in β-C and Chl a, whereas long-term HL acclimation significantly enhanced 14C labeling of Chl a but not β-C. Consequently, the maximal 14C signal ratio between β-C and Chl a was much lower in HL-grown plants (1:10) than in CL-grown plants (1:4). In lut5 mutants, containing α-carotene (α-C) together with reduced amounts of β-C, remarkably high 14C labeling was found for α-C while the labeling efficiency of Chl a was similar to that of wild-type plants. The maximum 14C ratios between carotenes and Chl a were 1:2 for α-C:Chl a and 1:5 for β-C:Chl a in CL-grown lut5 plants, suggesting high turnover of α-C. The data demonstrate continuous synthesis and degradation of carotenes and Chl a in photosynthesizing leaves and indicate distinct acclimatory responses of their turnover to changing irradiance. In addition, the results are discussed in the context of photosystem II repair cycle and D1 protein turnover.

Persistence of 14C-labeled atrazine and its residues in a field lysimeter soil after 22 years.

Twenty-two years after the last application of ring-14C-labeled atrazine at customary rate (1.7 kg ha(-1)) on an agriculturally used outdoor lysimeter, atrazine is still detectable by means of accelerated solvent extraction and LC-MS/MS analysis. Extractions of the 0-10 cm soil layer yielded 60% of the residual 14C-activity. The extracts contained atrazine (1.0 microg kg(-1)) and 2-hydroxy-atrazine (42.5 microg kg(-1)). Extractions of the material of the lowest layer 55-60 cm consisting of fine gravel yielded 93% of residual 14C-activity, of which 3.4 microg kg(-1) was detected as atrazine and 17.7 microg kg(-1) was 2-hydroxy-atrazine. The detection of atrazine in the lowest layer was of almost four times higher mass than in the upper soil layer. These findings highlight the fact that atrazine is unexpectedly persistent in soil. The overall persistence of atrazine in the environment might represent a potential risk for successive groundwater contamination by leaching even after 22 years of environmental exposure.

Metabolism and persistence of atrazine in several field soils with different atrazine application histories.

To assess the potential occurrence of accelerated herbicide degradation in soils, the mineralization and persistence of (14)C-labeled and nonlabeled atrazine was evaluated over 3 months in two soils from Belgium (BS, atrazine-treated 1973-2008; BC, nontreated) and two soils from Germany (CK, atrazine-treated 1986-1989; CM, nontreated). Prior to the experiment, accelerated solvent extraction of bulk field soils revealed atrazine (8.3 and 15.2 μg kg(-1)) in BS and CK soils and a number of metabolites directly after field sampling, even in BC and CM soils without previous atrazine treatment, by means of LC-MS/MS analyses. For atrazine degradation studies, all soils were incubated under different moisture conditions (50% maximum soil water-holding capacity (WHC(max))/slurried conditions). At the end of the incubation, the (14)C-atrazine mineralization was high in BS soil (81 and 83%) and also unexpectedly high in BC soil (40 and 81%), at 50% WHC(max) and slurried conditions, respectively. In CK soil, the (14)C-atrazine mineralization was higher (10 and 6%) than in CM soil (4.7 and 2.7%), but was not stimulated by slurried conditions. The results revealed that atrazine application history dramatically influences its degradation and mineralization. For the incubation period, the amount of extractable atrazine, composed of residues from freshly applied atrazine and residues from former field applications, remained significantly greater (statistical significance = 99.5 and 99.95%) for BS and CK soils, respectively, than the amount of extractable atrazine in the bulk field soils. This suggests that (i) mostly freshly applied atrazine is accessible for a complex microbial community, (ii) the applied atrazine is not completely mineralized and remains extractable even in adapted soils, and (iii) the microbial atrazine-mineralizing capacity strongly depends on atrazine application history and appears to be conserved on long time scales after the last application.

Atrazine Soil Core Residue Analysis from an Agricultural Field 21 Years after Its Ban

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) groundwater monitoring in the Zwischenscholle aquifer in western Germany revealed concentrations exceeding the threshold value of 0.1 μg L and increasing concentration trends even 20 yr after its ban. Accordingly, the hypothesis was raised that a continued release of bound atrazine residues from the soil into the Zwischenscholle aquifer in combination with the low atrazine degradation in groundwater contributes to elevated atrazine in groundwater. Three soil cores reaching down to the groundwater table were taken from an agricultural field where atrazine had been applied before its ban in 1991. Atrazine residues were extracted from eight soil layers down to 300 cm using accelerated solvent extraction and analyzed using liquid chromatography-tandem mass spectrometry. Extracted atrazine concentrations ranged between 0.2 and 0.01 μg kg for topsoil and subsoil, respectively. The extracted mass from the soil profiles represented 0.07% of the applied mass, with 0.01% remaining in the top layer. A complete and instantaneous remobilization of atrazine residues and vertical mixing with the groundwater body below would lead to atrazine groundwater concentrations of 0.068 μg L. Considering the area where atrazine was applied in the region and assuming instantaneous lateral mixing in the Zwischenscholle aquifer would result in a mean groundwater concentration of 0.002 μg L. A conservative estimation suggests an atrazine half-life value of about 2 yr for the soil zone, which significantly exceeds highest atrazine half-lives found in the literature (433 d for subsurface soils). The long-term environmental behavior of atrazine and its metabolites thus needs to be reconsidered.

DRY–WET CYCLES INCREASE PESTICIDE RESIDUE RELEASE FROM SOIL

Soil drying and rewetting may alter the release and availability of aged pesticide residues in soils. A laboratory experiment was conducted to evaluate the influence of soil drying and wetting on the release of pesticide residues. Soil containing environmentally long-term aged (9–17 years) 14C-labeled residues of the herbicides ethidimuron (ETD) and methabenzthiazuron (MBT) and the fungicide anilazine (ANI) showed a significantly higher release of 14C activity in water extracts of previously dried soil compared to constantly moistened soil throughout all samples (ETD: p < 0.1, MBT and ANI: p < 0.01). The extracted 14C activity accounted for 44% (ETD), 15% (MBT), and 20% (ANI) of total residual 14C activity in the samples after 20 successive dry–wet cycles, in contrast to 15% (ETD), 5% (MBT), and 6% (ANI) in extracts of constantly moistened soils. In the dry–wet soils, the dissolved organic carbon (DOC) content correlated with the measured 14C activity in the aqueous liquids and indicated a potential association of DOC with the pesticide molecules. Liquid chromatography MS/MS analyses of the water extracts of dry–wet soils revealed ETD and MBT in detectable amounts, accounting for 1.83 and 0.01%, respectively, of total applied water-extractable parent compound per soil layer. These findings demonstrate a potential remobilization of environmentally aged pesticide residue fractions from soils due to abiotic stresses such as wet–dry cycles. Environ. Toxicol. Chem. 2012; 31: 1941–1947.

Long-term persistence of various 14C-labeled pesticides in soils

The fate of the 14C-labeled herbicides ethidimuron (ETD), methabenzthiazuron (MBT), and the fungicide anilazine (ANI) in soils was evaluated after long-term aging (9-17 years) in field based lysimeters subject to crop rotation. Analysis of residual 14C activity in the soils revealed 19% (ETD soil; 0-10 cm depth), 35% (MBT soil; 0-30), and 43% (ANI soil; 0-30) of the total initially applied. Accelerated solvent extraction yielded 90% (ETD soil), 26% (MBT soil), and 41% (ANI soil) of residual pesticide 14C activity in the samples. LC-MS/MS analysis revealed the parent compounds ETD and MBT, accounting for 3% and 2% of applied active ingredient in the soil layer, as well as dihydroxy-anilazine as the primary ANI metabolite. The results for ETD and MBT were matching with values obtained from samples of a 12 year old field plot experiment. The data demonstrate the long-term persistence of these pesticides in soils based on outdoor trials.

Dynamics of transformation of the veterinary antibiotic sulfadiazine in two soils

Veterinary antibiotics administered to livestock can be unintentionally released into the environment, for example by the application of manure to soils. The fate of such antibiotics in soils is mostly determined by sorption and degradation processes, including transformation. There is a need to further examine the combined transformation and sorption behavior of these emerging pollutants in soils. Long-term batch sorption experiments with the (14)C-radiolabeled antibiotic sulfadiazine enabled us to simultaneously trace the sorption and transformation dynamics of sulfadiazine. The parent compound and the transformation products were analyzed in the liquid phase and in the extracts from the solid phase after a sequential extraction. We found that of up to six transformation products were formed during degradation and that these products exhibited quite different dynamics in the two soils. Transformation products were formed rapidly and were extractable from the solid phase. We observed identical sets of the transformation products in both phases. The input concentration influenced the course of transformation of the parent substance. We present a detailed analysis including a mathematical description and derive regulatory kinetic endpoints for predicting environmental concentrations.

Dissipation of bentazone, pyrimethanil and boscalid in biochar and digestate based soil mixtures for biopurification systems

Biopurification systems, such as biofilters, are biotechnological tools to prevent point sources of pesticide pollution stemming from on-farm operations. For the purification processes pesticide sorption and mineralization and/or dissipation are essential and both largely depend on the type of filling materials and the pesticide in use. In this paper the mineralization and dissipation of three contrasting (14)C-labeled pesticides (bentazone, boscalid, and pyrimethanil) were investigated in laboratory incubation experiments using sandy soil, biochar produced from Pine woodchips, and/or digestate obtained from anaerobic digestion process using maize silage, chicken manure, beef and pig urine as feedstock. The results indicate that the addition of digestate increased pesticide mineralization, whereby the mineralization was not proportional to the digestate loads in the mixture, indicating a saturation effect in the turnover rate of pesticides. This effect was in correlation with the amount of water extractable DOC, obtained from the digestate based mixtures. Mixing biochar into the soil generally reduced total mineralization and led to larger sorption/sequestration of the pesticides, resulting in faster decrease of the extractable fraction. Also the addition of biochar to the soil/digestate mixtures reduced mineralization compared to the digestate alone mixture but mineralization rates were still higher as for the biochar/soil alone. In consequence, the addition of biochar to the soil generally decreased pesticide dissipation times and larger amounts of biochar led to high amounts of non-extractable residues of pesticide in the substrates. Among the mixtures tested, a mixture of digestate (5%) and biochar (5%) gave optimal results with respect to mineralization and simultaneous sorption for all three pesticides.

Breakthrough dynamics of s-metolachlor metabolites in drinking water wells: Transport pathways and time to trend reversal

We present the results of a two years study on the contamination of the Luxembourg Sandstone aquifer by metolachlor-ESA and metolachlor-OXA, two major transformation products of s-metolachlor. The aim of the study was twofold: (i) assess whether elevated concentrations of both transformation products (up to 1000 ng/l) were due to fast flow breakthough events of short duration or the signs of a contamination of the entire aquifer and (ii) estimate the time to trend reversal once the parent compound was withdrawn from the market. These two questions were addressed by a combined use of groundwater monitoring, laboratory experiments and numerical simulations of the fate of the degradation products in the subsurface. Twelve springs were sampled weekly over an eighteen month period, and the degradation rates of both the parent compound and its transformation products were measured on a representative soil in the laboratory using a radiolabeled precursor. Modelling with the numeric code PEARL simulating pesticide fate in soil coupled to a simple transfer function model for the aquifer compartment, and calibrated from the field and laboratory data, predicts a significant damping by the aquifer of the peaks of concentration of both metolachlor-ESA and -OXA leached from the soil. The time to trend reversal following the ban of s-metolachlor in spring protection zones should be observed before the end of the decade, while the return of contaminant concentrations below the drinking water limit of 100 ng/l however is expected to last up to twelve years. The calculated contribution to total water discharge of the fast-flow component from cropland and short-circuiting the aquifer was small in most springs (median of 1.2%), but sufficient to cause additional peaks of concentration of several hundred nanograms per litre in spring water. These peaks are superimposed on the more steady contamination sustained by the base flow, and should cease immediately once application of the parent compound stops.