A whole-genome assembly of Drosophila.

We report on the quality of a whole-genome assembly of Drosophila melanogaster and the nature of the computer algorithms that accomplished it. Three independent external data sources essentially agree with and support the assembly's sequence and ordering of contigs across the euchromatic portion of the genome. In addition, there are isolated contigs that we believe represent nonrepetitive pockets within the heterochromatin of the centromeres. Comparison with a previously sequenced 2.9- megabase region indicates that sequencing accuracy within nonrepetitive segments is greater than 99. 99% without manual curation. As such, this initial reconstruction of the Drosophila sequence should be of substantial value to the scientific community.

Aquatic risk assessment of a polycarboxylate dispersant polymer used in laundry detergents.

Polycarboxylates enhance detergent soil removal properties and prevent encrustation of calcium salts on fabrics during washing. Laundry wastewater typically reaches wastewater treatment plants, which then discharge into aquatic environments. The yearly average concentration of a 4500 molecular weight (MW) sodium acrylate homopolymer reaching U.S. wastewater treatment plants will be approximately 0.7 mg/L. Publications showing the low to moderate acute aquatic toxicity of polycarboxylates are readily available. However, there are no published evaluations that estimate wastewater removal and characterize the probability of exceedance of acceptable chronic aquatic exposure. WW-TREAT can be used to estimate removal during wastewater treatment and PG-GRIDS can be applied to characterize risk for exceedance in wastewater treatment plant outfalls. After adjustments for the MW distribution of the homopolymer, WW-TREAT predicted that 6.5% will be removed in primary treatment plants and 60% will be removed in combined primary and activated sludge treatment plants. These estimates are consistent with wastewater fate tests, but underestimate homopolymer removal when homopolymer precipitation is included. Acceptable levels of chronic outfall (receiving water) exposure were based on aquatic toxicity testing in algae, fish, and Daphnia magna. PG-GRIDS predicted that no unreasonable risk for exceedance of acceptable chronic exposure will occur in the outfalls of U.S. wastewater plants. Future development of wastewater treatment models should consider polymer MW distribution and precipitation as factors that may alter removal of materials from wastewater.

Polymers as Solid Waste in Municipal Landfills.

Synthetic polymers reach municipal landfills as components of products such as waste household paints, packaging films, storage containers, carpet fibers, and absorbent sanitary products. Some polymers in consumer products that reach landfills are designed to photodegrade or biodegrade. This article examines the significance of degradable polymers in management of solid waste in municipal landfills. Most landfills are not designed to photodegrade or biodegrade solid waste. Landfill disposal of stable polymers such as polyacrylics and polyethylenes is not associated with significant polymer degradation or mobility. Stability to photodegradation and biodegradation is an advantage when municipal landfills are used for disposal of polymer products as solid waste. Use of landfill disposal can be a responsible means to manage polymer waste and can be part of an overall waste management plan which includes source reduction, recycling, reuse, composting, and waste-to-energy incineration.

Aquatic toxicity of acrylates and methacrylates: quantitative structure-activity relationships based on Kow and LC50.

Recent EPA scrutiny of acrylate and methacrylate monomers has resulted in restrictive consent orders and Significant New Use Rules under the Toxic Substances Control Act, based on structure-activity relationships using mouse skin painting studies. The concern is centered on human health issues regarding worker and consumer exposure. Environmental issues, such as aquatic toxicity, are still of concern. Understanding the relationships and environmental risks to aquatic organisms may improve the understanding of the potential risks to human health. This study evaluates the quantitative structure-activity relationships from measured log Kow's and log LC50's for Pimephales promelas (fathead minnow) and Carassius auratus (goldfish). Scientific support of the current regulations is also addressed. Two monomer classes were designated: acrylates and methacrylates. Spearman rank correlation and linear regression were run. Based on this study, an ecotoxicological difference exists between acrylates and methacrylates. Regulatory activities and scientific study should reflect this difference.

Validation trial of predictive fate models using an aquatic herbicide (endothall).

Environmental risk assessment of pesticides in aquatic environments requires predictions of their persistence and compartmentalization. A strategy for developing confidence in predictive fate models, such as the Exposure Analysis Modeling System (EXAMS) and the Simplified Lake and Stream Analysis model (SLSA), is to test the models using carefully chosen chemicals in semi-controlled and field situations. For example, endothall, a relatively water-soluble aquatic herbicide, essentially has a sole fate process, biotransformation. This dicarboxylic acid was used to test the predictive capabilities of EXAMS and SLSA and to identify sources of variance in those predictions. The models were parameterized using laboratory, experimental pool and field measurements. Persistence and compartmentalization of endothall in the water, sediments and aquatic plants (Eurasian watermilfoil-Myriophyllum spicatum L.) contained in experimental pools were measured using gas chromatography. Both EXAMS and SLSA predicted aqueous compartment half-lives ranging from 7.3 to 7.8 d, whereas an aqueous half-life of 4 d was observed in the experimental pools. Endothall was introduced to areas within Pat Mayse Lake, a 2,400-ha reservoir in north central Texas, as part of an aquatic plant management program for M. spicatum. Concentrations of endothall were below detection limits (0.002 mg L-1 water, 0.01 mg kg-1 sediment) in 2 to 3 d and in 4 d in the water and sediment compartments, respectively. EXAMS and SLSA predicted half-lives ranging from 3 to 6 d in the water column. Observed aqueous half-lives ranged from 0.1 to 0.23 d. Horizontal dispersion and dilution contributed significantly to the dissipation of endothall at these sites. Predicted concentrations of endothall in sediment were similar to the measured concentrations. This study is one validation trial of EXAMS and SLSA in which the models were not considered validated.

Compartmentalization and persistence of endothall in experimental pools.

The compartmentalization and persistence of endothall, an aquatic herbicide, was studied using static greenhouse experimental pools. An overall aqueous pseudo-first-order decay rate coefficient of 0.173 day-1 and a half-life of 4.01 days were observed at endothall treatment levels of 0.03, 1.6, and 4.5 mg liter-1. Instantaneous sediment partition coefficients (Kp) were calculated at maximum endothall concentrations in sediments and ranged from 51.4 to 127.7. Bioconcentration factors (BCF) for the submerged aquatic macrophyte, Myriophyllum spicatum, ranged from 3.9 to 768.9. These instantaneous BCF values were calculated at the maximum M. spicatum endothall concentrations. The short aqueous half-life for endothall compares well with previous studies; however, both the Kp and BCF were one to three orders of magnitude higher than observed in a previous laboratory study and calculated from regression equations based on endothall solubility. Experimental pool studies can be important steps in translation of data from the laboratory to field and in the development of field sampling protocols that require understanding of expected behavior of a chemical in aquatic systems.