Boron contamination and its risk management in terrestrial and aquatic environmental settings

Boron (B) is released to terrestrial and aquatic environments through both natural and anthropogenic sources. This review describes the current knowledge on B contamination in soil and aquatic environments in relation to its geogenic and anthropogenic sources, biogeochemistry, environmental and human health impacts, remediation approaches, and regulatory practices. The common naturally occurring sources of B include borosilicate minerals, volcanic eruptions, geothermal and groundwater streams, and marine water. Boron is extensively used to manufacture fiberglass, thermal-resistant borosilicate glass and porcelain, cleaning detergents, vitreous enamels, weedicides, fertilizers, and B-based steel for nuclear shields. Anthropogenic sources of B released into the environment include wastewater for irrigation, B fertilizer application, and waste from mining and processing industries. Boron is an essential element for plant nutrition and is taken up mainly as boric acid molecules. Although B deficiency in agricultural soils has been observed, B toxicity can inhibit plant growth in soils under arid and semiarid regions

Aerial deposition at two research stations in Hungary

The composition of precipitation and element loads originating from rainwater were examined monthly between 2005 and 2008 at two experimental stations (Őrbottyán in the Danube–Tisza Interfluve region and Nagyhörcsök in the Mezőföld region of Hungary) of the Research Institute for Soil Science and Agricultural Chemistry (RISSAC) of the Hungarian Academy of Sciences. Twenty-five characteristics were analysed: pH, EC, NO3 -N, NH4 -N, and concentrations of the main macro- and microelements. The observation represents the dry and wet deposition together. Measurements were carried out by ICP-OES device, with the exception of carbonate, chloride, ammonia and nitrate. The main results can be summarized as follows: – Generally, the lower amounts of monthly precipitation resulted in higher EC, pH; NH4-N, Ca, Na and K concentrations. The highest element yields, however, were typical of the wet months. Acidic precipitation (below pH 5) was rich in nitric acid forming NO3 -N, but poor in NH4 -N at the Őrbottyán Experimental Station. Emission of the nearby cement works in February and March 2006 caused an order of magnitude higher increase in Ca, Mg, Na and Sr elements as compared to other months, and there was a considerable rise in the NH4 -N, S, Zn, As, Cr and Pb concentrations of the precipitation (Table 5, 1st half of the year). The pH reached 7.0 at this site. – Depositions were small at the Nagyhörcsök Experimental Station in winter. During the warmer months (May, June and July) the NH4 -N concentration was 10–20 times higher than the NO3-N concentration. The neighbouring fertile and humus rich soils, fertilization, as well as the nearby animal husbandry farm make notable NH3 emission. In this period the concentration of NH4 -N and the alkalizing cations Ca and K raised the precipitation’s pH, and the pH increased from January to June. – Aerial deposition varied greatly at both sites, representing the following values in kg·ha-1 ·year-1 unit: NO3 -N 5–20; NH4 -N 10–31; total N 30–48; Ca 6–60; K 6–16; S 2–21; Na 4–13; Mg 2–16; P 2–6. The deposition of Zn, Mn, Fe, Cu and B elements at these sites were similar to previous Hungarian and Austrian data. Pb, Ni, Cd and Co depositions, however, were an order of magnitude lower, which demonstrates the positive result of the successful control of heavy metal pollution in Europe since 1990. – Aerial deposition has considerable agronomical and environmental significance. According to the present study, aerial deposition could satisfy 10% K, 15% Mg, 20% P, 30% Ca and N, 40% S element demand of an average 5 t·ha-1 grain and 5 t·ha-1 straw yield of cereals on the chernozem soil of the Nagyhörcsök Station. When using combine harvesting, the straw remains on the site and only the grain is removed, so 25% P, 45% K, 100–300% S and Ca, and several fold of Na-requirement could be covered by the aerial deposition. – Atmospheric deposition may more or less compensate the amount of Mo, Ni and Se built in by grain, while the Zn requirement might be exceeded by about 60%. The deposition of B, Ba, Cu and Sr is several times higher than the amount built in by the grain yield. Aerial fertilization with Cu, Mo, Se and Zn seems to be advantageous, as the site is poor in Zn and Cu, or not satisfactorily supplied with Mo and Se elements. Cd, Hg and Pb loads, however, are environmentally disadvan-tageous, especially on the long-term. The latter harmful heavy metals can also get into waters, on the surface of crops and can cause direct damage to the food chain. – The following minimal – maximal depositions were measured on the two experimental sites: Zn 112–1391; Sr 30–202; Cu 21–153; Fe 42–119; Ba 40–79; Mn 33–62; B 0–33; Pb 2–4; Ni, Cr and Mo 0–6; As 0–4; Hg 0–1.5; Co 0.4–0.7; Cd 0–0.3 g·ha-1 year-1 . The pH varied between 4.2 and 7.0 while electrical conductivity ranged between 25 and 1996 μS·cm-1