Nicolai David Jablonowski

Still present after all these years: persistence plus potential toxicity raise questions about the use of atrazine

As one of the worlds’ most heavily applied herbicides, atrazine is still a matter of controversy. Since it is regularly found in ground and drinking water, as well as in sea water and the ice of remote areas, it has become the subject of continuous concern due to its potential endocrine and carcinogenic activity. Current findings prove long-held suspicions that this compound persists for decades in soil. Due to the high amount applied annually all over the world, the soil burden of this compound is considered to be tremendous, representing a potential long-term threat to the environment. The persistence of chemicals such as atrazine has long been underestimated: Do we need to reconsider the environmental risk?

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.

Priority Effects of Time of Arrival of Plant Functional Groups Override Sowing Interval or Density Effects : A Grassland Experiment

Priority effects occur when species that arrive first in a habitat significantly affect the establishment, growth, or reproduction of species arriving later and thus affect functioning of communities. However, we know little about how the timing of arrival of functionally different species may alter structure and function during assembly. Even less is known about how plant density might interact with initial assembly. In a greenhouse experiment legumes, grasses or forbs were sown a number of weeks before the other two plant functional types were sown (PFT) in combination with a sowing density treatment. Legumes, grasses or non-legume forbs were sown first at three different density levels followed by sowing of the remaining PFTs after three or six-weeks. We found that the order of arrival of different plant functional types had a much stronger influence on aboveground productivity than sowing density or interval between the sowing events. The sowing of legumes before the other PFTs produced the highest aboveground biomass. The larger sowing interval led to higher asymmetric competition, with highest dominance of the PFT sown first. It seems that legumes were better able to get a head-start and be productive before the later groups arrived, but that their traits allowed for better subsequent establishment of non-legume PFTs. Our study indicates that the manipulation of the order of arrival can create priority effects which favour functional groups of plants differently and thus induce different assembly routes and affect community composition and functioning.

Phosphorus from wastewater to crops: An alternative path involving microalgae

Phosphorus (P) is a non-renewable resource, a major plant nutrient that is essential for modern agriculture. Currently, global food and feed production depends on P extracted from finite phosphate rock reserves mainly confined to a small number of countries. P limitation and its potential socio-economic impact may well exceed the potential effects of fossil fuel scarcity. The efficiency of P usage today barely reaches 20%, with the remaining 80% ending up in wastewater or in surface waters as runoff from fields. When recovered from wastewater, either chemically or biologically, P is often present in a form that does not meet specifications for agricultural use. As an alternative, the potential of microalgae to accumulate large quantities of P can be a way to direct this resource back to crop plants. Algae can acquire and store P through luxury uptake, and the P enriched algal biomass can be used as bio-fertilizer. Technology of large-scale algae cultivation has made tremendous progress in the last decades, stimulated by perspectives of obtaining third generation biofuels without requiring arable land or fresh water. These new cultivation technologies can be used for solar-driven recycling of P and other nutrients from wastewater into algae-based bio-fertilizers. In this paper, we review the specifics of P uptake from nutrient-rich waste streams, paying special attention to luxury uptake by microalgal cells and the potential application of P-enriched algal biomass to fertilize crop soils.

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.

Biochar-Mediated [14C]Atrazine Mineralization in Atrazine-Adapted Soils from Belgium and Brazil

Biochar addition to soil has been reported to reduce the microbial degradation of pesticides due to sorption of the active compound. This study investigated whether the addition of hardwood biochar alters the mineralization of (14)C-labeled atrazine in two atrazine-adapted soils from Belgium and Brazil at different moisture regimens. Biochar addition resulted in an equally high or even in a significantly higher atrazine mineralization compared to the soils without biochar. Statistical analysis revealed that the extent of atrazine mineralization was more influenced by the specific soil than by the addition of biochar. It was concluded that biochar amendment up to 5% by weight does not negatively affect the mineralization of atrazine by an atrazine-adapted soil microflora.

Spatial Distribution and Characterization of Long-Term Aged 14C-Labeled Atrazine Residues in Soil

The long-term behavior of the herbicide atrazine and its metabolites in the environment is of continued interest in terms of risk assessment and soil quality monitoring. Aqueous desorption, detection, and quantification of atrazine and its metabolites from an agriculturally used soil were performed 22 years after the last atrazine application. A lysimeter soil containing long-term aged atrazine for >20 years was subdivided into 10 and 5 cm layers (at the lysimeter bottom: soil 0-50 and 50-55 cm; fine gravel 55-60 cm depth, implemented for drainage purposes) to identify the qualitative and quantitative differences of aged (14)C-labeled atrazine residues depending on the soil profile and chemico-physical conditions of the individual soil layers. Deionized water was used for nonexhaustive cold water shaking extraction of the soil. With increasing soil depth, the amount of previously applied (14)C activity decreased significantly from 8.8% to 0.7% at 55-60 cm depth whereas the percentage of desorbed (14)C residues in each soil layer increased from 2% to 6% of the total (14)C activity in the sample. The only metabolite detectable by means of LC-MS/MS was 2-hydroxyatrazine while most of the residual (14)C activity was bound to the soil and was not desorbed. The amount of desorbed 2-hydroxyatrazine decreased with increasing soil depth from 21% to 10% of the total desorbed (14)C residue fraction. The amount of (14)C residues in the soil layers correlated well with the carbon content in the soil and in the aqueous soil extracts ( p value = 0.99 and 0.97, respectively), which may provide evidence of the binding behavior of the aged atrazine residues on soil carbon. The lowest coarse layer (55-60 cm) showed increased residual (14)C activity leading to the assumption that most (14)C residues were leached from the soil column over time.

Accelerated Degradation of 14C-Atrazine in Brazilian Soils from Different Regions

The repeated use of a given pesticide may induce a selection of the soil microbial population, resulting in a rapid degradation of the respective xenobiotic. Patterns of atrazine degradation (mineralization, formation of metabolites and nonextractable residues (NER)) were evaluated in two Brazilian soils with a history of atrazine application. Results were compared with those obtained from soils that had no agricultural use or herbicide application history. (14)C-Atrazine mineralization in unsaturated treated soils was high. By the 85th day of incubation, 82% of the applied (14)C-atrazine was mineralized in the Rhodic Hapludox and 74% in the Xanthic Haplustox. Mineralization remained low in nontreated soils (<or=5.1%). Incubation under slurry conditions enhanced atrazine mineralization in the treated Xantic Haplustox and surprisingly also in the nontreated Rhodic Hapludox (98 and 83% on the 85th day, respectively), whereas in the other samples the evolved (14)CO(2) did not differ (p < 0.05) from the unsaturated conditions. The water-extractable amount of atrazine directly after (14)C-atrazine application was higher in both Xanthic Haplustox samples (around 80% of applied atrazine) in comparison to the Rhodic Hapludox samples (around 60%). Extractable activity and the formation of metabolites and NER varied among the studied soils according to the atrazine application history rather than the soil characteristics.

Valorization of Sida ( Sida hermaphrodita ) biomass for multiple energy purposes

The performance and biomass yield of the perennial energy plant Sida hermaphrodita (hereafter referred to as Sida) as a feedstock for biogas and solid fuel was evaluated throughout one entire growing period at agricultural field conditions. A Sida plant development code was established to allow comparison of the plant growth stages and biomass composition. Four scenarios were evaluated to determine the use of Sida biomass with regard to plant development and harvest time: (i) one harvest for solid fuel only; (ii) one harvest for biogas production only; (iii) one harvest for biogas production, followed by a harvest of the regrown biomass for solid fuel; and (iv) two consecutive harvests for biogas production. To determine Sidas value as a feedstock for combustion, we assessed the caloric value, the ash quality, and melting point with regard to DIN EN ISO norms. The results showed highest total dry biomass yields of max. 25 t ha−1, whereas the highest dry matter of 70% to 80% was obtained at the end of the growing period. Scenario (i) clearly indicated the highest energy recovery, accounting for 439 288 MJ ha−1; the energy recovery of the four scenarios from highest to lowest followed this order: (i) ≫ (iii) ≫ (iv) > (ii). Analysis of the Sida ashes showed a high melting point of >1500 °C, associated with a net calorific value of 16.5–17.2 MJ kg−1. All prerequisites for DIN EN ISO norms were achieved, indicating Sidas advantage as a solid energy carrier without any post‐treatment after harvesting. Cell wall analysis of the stems showed a constant lignin content after sampling week 16 (July), whereas cellulose had already reached a plateau in sampling week 4 (April). The results highlight Sida as a promising woody, perennial plant, providing biomass for flexible and multipurpose energy applications.

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.