Concentrations of some elements in and on Scots pine needles

Abstract

Elemental concentrations in needles from individual Scots pine trees (Pinus sylvestris L.) from four different sites in Latvia were determined. P, S, K, Ca, Mn, Fe, Cu, Zn, Rb and Sr were simultaneously determined by total-reflection x-ray fluorescence and Cr, Co, Ni, Cd, Pb were measured using multi-element graphite furnace atomic absorption spectrometry. The elemental concentrations obtained after washing the pine needles with water and with chloroform were compared with those obtained without washing. Chloroform was a more effective washing agent for the removal of airborne deposits from the surface of the needles. The comparison of the chemical compositions of pine needles that were unwashed or washed with chloroform allowed the trace elements in and on the needles to be distinguished for an evaluation of the character of pollution.

Review: use of conifer needles as passive samplers of inorganic pollutants in air quality monitoring

“…The ratio between the two contributions for each element depends on: parameters related to conifer metabolism; the function of the polluting element in vegetal tissue growth; the biodynamic behavior of the element during needle aging; the seasonal cycle (less important than aging); and environmental parameters, such as the concentration of the heavy metal in the soil and its availability to the conifer, and the concentration in atmospheric PM. P, S, K, Ca, Mn, Zn and Cd are mainly from the roots, 56,57 but once in the needle they have different biodynamic behaviors with aging. P and K are easily transferred to new tissues and therefore tend to show decreasing concentrations in older needles with respect to current year needles.…”

“…48,58 In contrast, Cu, Cr, Pb, Ni, Co and especially Fe are mainly of atmospheric provenance. 56,57,59,60 Fe, with reference to 1 g of dry needles, has been estimated to increase on the surface of the needles at a rate of 17 mg per year, which gives surface amounts in the range 21-65 ppm. 61 Once on the needle, the mean residence time of Fe is 1.6 years because it has a weathering half-life of 1.1 years.…”

“…These short wash and rinse periods avoid the leaching of certain elements (N, B, K, Cl) from the tissues of the needles. 60,65 Alternatively, Viksna et al 57 placed the needles in a 75 mL plastic tube into which they poured 40 mL of washing solution. The tube was closed and shaken for 1 min.…”

“…Many workers 11,38,[67][68][69] have used tap or distilled, deionized water as washing agent and were satised with their water-washing procedure as they noticed a decrease in element concentrations in a polluted site of about 28-74% compared with unwashed samples. 68 However, other workers 50,57 observed that it is not sufficient to use water to prepare the washed subsample as this will only remove the water-soluble particles and substances. Moreover, the needles have generally been exposed to rain, possibly for long periods of time before sampling, so that most of the water-removable contaminants, with the exception of those entrapped by the hydrophobic epicuticular wax, may no longer be present on the needle surface.…”

“…Acids, fat-dissolving agents or chelating agents can be alternatively used as these are all able to dissolve the epicuticular wax and thus also remove the elements trapped in this layer. Solvents used have included: butyl alcohol (C 4 H 9 OH), 5 carbon tetrachloride (CCl 4 ), 59 acetone (C 3 H 6 O), 66 ethylenediaminetetraacetic acid (EDTA) 57 and a (1 : 1 v/v) solution of tetrahydrofuran-toluene. 50 This latter solvent might be taken as the most popular as it is cited in many papers.…”