Microplastic extraction efficency from soil depends on soil compostion.

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A microwave digestion procedure was developed for multi-element determinations in tree foliage by inductively coupled plasma–atomic emission spectrometry. The procedure involved the sequential digestion of 0.500 g of plant material with HNO3 (10 mL), H2O2 (1 mL), and HCl (2 mL) at 90% power for 30 min, 90% power for 15 min, and 30% power for 10 min, respectively. The proposed method gave Ca, Mg, K, Na, Mn, P, and S results in good agreement with the National Institute of Standards and Technology plant reference materials. Iron and aluminum concentrations were 20 to 30% lower than the certified National Institute of Standards and Technology values. Recovery of standard additions of the elements tested (including iron and aluminum) ranged from 93 to 105%. The proposed digestion method provides accurate and precise results for multi-element analysis on one solution. In addition, HClO4, an extreme laboratory hazard, has been replaced in the digestion procedure by H2O2. The microwave digestion method has been used successfully in our laboratory for over 1 year for routine analysis and for a quality assurance program using a variety of plant materials. With this method 36 to 48 samples per person per day can be prepared for inductively coupled plasma–atomic emission spectrometry analysis.

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Little information exists on the accuracy, precision, and make‐up of extractable S in surface organic horizons of forest soils. Eight extractants (H2O, 0.01 M CaCl2, 0.01 M KCl, 0.01 M LiCl, 0.003 M NH4OAc, 0.003 and 0.01 M NH4Cl, and 500 mg P L−1 as Ca(H2PO4)2·H2O) were evaluated for the extraction and determination of SO4‐S and total extractable S in surface organic horizons of five forest soils. The analyses for SO4‐S and total extractable S were performed by ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP‐AES), respectively. Each of the weak salt extractants removed similar amounts of SO4‐S and total extractable S. Water was the least desirable extractant because it removed more organic S than the salt extractants, was the most variable for IC analysis, and produced inconsistent results. The 0.01 M NH4Cl extractant, however, was found to be the most consistent extractant. The precision ranged from 3.7 to 8.9% for the IC analyses excluding the aspen (Populus tremuloides Michx.) sample and from 1.9 to 8.4% for the ICP‐AES analyses. Poor precision in the SO4‐S determination of the aspen organic horizon was due to the elution of an unidentified peak adjacent to the S peak. Quantitative recoveries from 102 to 108% and from 97 to 108% were obtained in the 0.01 M NH4Cl extract by the IC and ICP‐AES methods, respectively. The effect of varying solution to soil ratios was also determined for 0.01 M NH4Cl. The 10:1 solution to soil ratio was the most consistent. Ratios <10:1 had significantly lower concentrations of extractable S and SO4‐S for three soils and caused logistical problems in the laboratory (i.e., slower filtering, more sample required) because of the low solutin‐to‐soil ratio. Storage of airdried material at room temperature (20 ± 4 °C) for 1.5 yr resultd in increased total extractable S and SO4‐S concentrations.