Impacts of soil use and management on water quality in agricultural watersheds in Southern Brazil.

Worldwide, agriculture is considered one of the main activities that influence water quality. The objective of this work was to evaluate the influence of soil use and management on water quality at the small watershed scale, in Southern Brazil. One watershed is characterized by production of annual crop seeds under no-tillage (zero tillage), with crop rotation and with terraces (Sarandi watershed?SW), while the other is characterized by production of grains in the summer and pasture with grazing in the winter, under no-tillage, without crop rotation and without terraces (Coxilha watershed?CW). Flow and climatic data were measured during 2 years. Water samples were manually taken at precipitation events and base flow over 1 year for laboratory analysis. During events of high volume, most of the rainfall was converted to base flow in SW, while in CW, most of the rainfall was transformed into overland flow. Overall, higher concentrations and losses of sediments and nutrients occurred in the CW, mainly during precipitation events in the winter crops season. Of the total nitrogen concentration in water, approximately 3% was ammonium-N and 58% was nitrate-N, on average, in both watersheds. For total phosphorus concentration in water, more than 75% was particulate in both watersheds, however, the bioavailable phosphorus accounted for 70% of the total phosphorus in the SW and for 35% in the CW. The higher concentration of bioavailable phosphorus in the SW indicates a short-term pollution potential, but in both watersheds, the water quality was impaired by the high concentrations of total phosphorus. In general, even with no-tillage, the results highlight the importance of best management practices as terracing, riparian vegetation, crop rotation, better crop systems and fertilizer management to avoid degradation of water resources

Determination of sunscreen compounds in water samples by silicone rod extraction

Silicone rod extraction (SR) is a siloxane-based methodology for the extraction of organic pollutants from aqueous samples with similar principle extraction as the stir bar sorptive extraction (SBSE). In this study the SR was coupled with HPLC-DAD and employed for the extraction and quantification of selected UV filters in water and seawater samples. Chromatographic parameters were optimized as well as the main sorption/desorption conditions for 4-methylbenzylidene camphor (4MBC) and octyl-methoxy cinnamate (OMC) from both river water and seawater samples. After optimization of the proposed method the following variables were selected: 25,0 mL of sample volume, 3 hour extraction, 1250 rpm as stirring velocity and 2 mL methanol as desorption solvent. The recoveries from seawater samples were 76.6% for 4MBC and 85.9% OMC. In river water samples recoveries of 69.8% and 82.4 % for 4MBC and OMC, respectively, were observed when salt was added to the sample. Linear calibration curves were o

Experimental chemistry a laboratory manual for principles of chemistry

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Arsenic contamination of natural waters in San Juan and La Pampa, Argentina

Arsenic (As) speciation in surface and groundwater from two provinces in Argentina (San Juan and La Pampa) was investigated using solid phase extraction (SPE) cartridge methodology with comparison to total arsenic concentrations. A third province, Río Negro, was used as a control to the study. Strong cation exchange (SCX) and strong anion exchange (SAX) cartridges were utilised in series for the separation and preservation of arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MAV) and dimethylarsinic acid (DMAV). Samples were collected from a range of water outlets (rivers/streams, wells, untreated domestic taps, well water treatment works) to assess the relationship between total arsenic and arsenic species, water type and water parameters (pH, conductivity and total dissolved solids, TDS). Analysis of the waters for arsenic (total and species) was performed by inductively coupled plasma mass spectrometry (ICP-MS) in collision cell mode. Total arsenic concentrations in the surface and groundwater from Encon and the San José de Jáchal region of San Juan (north-west Argentina within the Cuyo region) ranged from 9 to 357 μg l−1 As. Groundwater from Eduardo Castex (EC) and Ingeniero Luiggi (LU) in La Pampa (central Argentina within the Chaco-Pampean Plain) ranged from 3 to 1326 μg l−1 As. The pH range for the provinces of San Juan (7.2–9.7) and La Pampa (7.0–9.9) are in agreement with other published literature. The highest total arsenic concentrations were found in La Pampa well waters (both rural farms and pre-treated urban sources), particularly where there was high pH (typically > 8.2), conductivity (>2,600 μS cm−1) and TDS (>1,400 mg l−1). Reverse osmosis (RO) treatment of well waters in La Pampa for domestic drinking water in EC and LU significantly reduced total arsenic concentrations from a range of 216–224 μg l−1 As to 0.3–0.8 μg l−1 As. Arsenic species for both provinces were predominantly AsIII and AsV. AsIII and AsV concentrations in San Juan ranged from 4–138 μg l−1 to <0.02–22 μg l−1 for surface waters (in the San José de Jáchal region) and 23–346 μg l−1 and 0.04–76 μg l−1 for groundwater, respectively. This translates to a relative AsIII abundance of 69–100% of the total arsenic in surface waters and 32–100% in groundwater. This is unexpected because it is typically thought that in oxidising conditions (surface waters), the dominant arsenic species is AsV. However, data from the SPE methodology suggests that AsIII is the prevalent species in San Juan, indicating a greater influence from reductive processes. La Pampa groundwater had AsIII and AsV concentrations of 5–1,332 μg l−1 and 0.09–592 μg l−1 for EC and 32–242 μg l−1 and 30–277 μg l−1 As for LU, respectively. Detectable levels of MAV were reported in both provinces up to a concentration of 79 μg l−1 (equating to up to 33% of the total arsenic). Previously published literature has focused primarily on the inorganic arsenic species, however this study highlights the potentially significant concentrations of organoarsenicals present in natural waters. The potential for separating and preserving individual arsenic species in the field to avoid transformation during transport to the laboratory, enabling an accurate assessment of in situ arsenic speciation in water supplies is discussed