P. M. Rutherford

Environmental impacts of phosphogypsum

Abstract Phosphogypsum is an acidic by-product from the phosphate fertilizer industry. Large quantities are produced world-wide and it is estimated that by the year 2000 up to 280 million tonnes will be produced annually. Although phosphogypsum is mainly calcium sulfate dihydrate, it contains elevated levels of impurities which originate primarily from the source phosphate rock used in P fertilizer production. The main environmental concerns associated with phosphogypsum are: (i) movement of fluoride, sulfate, total dissolved solids, certain trace elements, and radionuclides from the U-238 decay series below phosphogypsum stacks into groundwater supplies; (ii) radon-222 exhalation which may pose a health risk to workers on the site or people living close to stacks; (iii) acidity; and (iv) radon-222 exhalation from soil into residential homes when agricultural land previously treated with phosphogypsum is converted to residential usage. In order to fully understand the environmental impact of phosphogypsum, it is necessary to understand the geochemical and hydrological processes that control the composition of phosphogypsum leachates and the attenuation of environmentally sensitive chemical species when these leachates enter soil environments. This article will review the chemistry of phosphogypsum and the environmental concerns associated with phosphogypsum that is stockpiled in waste repositories or is used as an agricultural soil amendment.

Influence of texture on habitable pore space and bacterial-protozoan populations in soil

SummarySoil texture affects pore space, and bacterial and protozoan populations in soil. In the present study we tested the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils because they have a larger volume of protected pore space available to them. The experiment consisted of three sterilized Orthic Black Chernozemic soils (silty clay, clay loam, and sandy loam) inoculated with bacteria, two treatments (with and without protozoa), and five sampling dates. The soils were amended with glucose and mineral N on day 0. On day 4 bacterial numbers in all three soils were approximately 3×109 g−1 soil. The greatest reduction in bacteria due to protozoan grazing occurred between day 4 and day 7. Compared to the treatment without protozoa, bacteria in the treatment with protozoa were reduced by 68, 50, and 75% in the silty clay, clay loam, and sandy loam, respectively. On day 4, 2 days after the protozoan inoculation, all protozoa were active. The numbers were 10330, 4760, and 15 380 g−1 soil for the silty clay, clay loam, and sandy loam, respectively. Between day 4 and day 7, the period of greatest bacterial decline, total protozoa increased greatly to 150480, 96160, and 192100 g−1 soil for the three soils, respectively. Most protozoa encysted by day 7. In all soils the addition of protozoa significantly increased CO2−C evolution per g soil relative to the treatment without protozoa. Our results support the hypothesis that bacteria are more protected from protozoan predation in fine-textured soils than in coarse-textured soils.

Heterogeneous distribution of trace elements and fluorine in phosphogypsum by-product

Phosphogypsum (PG), a by-product from phosphate fertilizer production, is composed mainly of gypsum (CaSO 4 .2H 2 O) but also contains minor quantities of trace elements (TE), rare earth elements (REE) and F. Some elements may be elevated in quantities to be of environmental concern. This study determined the distribution of TE, REE and F among three size fractions ( 53 μm) in PGs derived from three different phosphate rock sources. Fine fraction PG (<20 μm) composed of <10% of total PG mass but was highly enriched in TE, REE and F compared to unfractionated PG. For PG derived from Idaho rock, Se in the fine fraction was enriched 830 times over soil and 415 times over shale while Cd was enriched in the fine fraction 70-fold over shale and soil. Fluorine was elevated 37 times in the fine fraction compared to shale. The same trends were observed for PG derived from Togo and Florida rocks. Elevated elemental concentrations in fine particles and particle sorting during PG deposition may contribute to chemical heterogeneity of PG repositories, and make elements more susceptible to mobilization processes, such as leaching and erosion. Removal of fines will improve the utilization of PG in other industries, such as for use as an amendment to agricultural soils

Heterogeneous distribution of radionuclides, barium and strontium in phosphogypsum by-product

Phosphogypsum (PG) is a high volume by-product of the phosphate fertilizer industry which is composed mainly of CaSO4·2H2O. Impurities in PG include F, trace elements and naturally-occurring radionuclides. Radium-226 content is sufficiently high in some PGs that it has limited PG usage in building materials and as an amendment to agricultural soils. Radium likely exists in PG as a sulfate solid solution with Ba, and possibly Sr. This study determined the distribution of 226Ra, Ba, Sr, U, Th and 210Pb among three size fractions (fine: 53 μm) in PGs derived from three different phosphate rock sources. All chemical species, except for Sr in PG derived from Idaho rock, were enriched in the <20-μm fraction relative to the other size fractions and relative to unfractionated PG. On average, fine fraction 226Ra and 210Pb contents were enriched approximately sixfold over unfractionated PG. 226Ra was enriched in the fine fraction to a greater degree than were Ba or Sr, indicating that Ra behavior in PG is distinct from these other elements. The combination of (i) particle sorting during PG deposition, and (ii) non-uniform distribution of radionuclides in PG, may contribute to radionuclide heterogeneity at PG repositories.

Radioactivity and elemental composition of phosphogypsum produced from three phosphate rock sources

Phosphogypsum, a by-product of phosphate fertilizer production, is produced in large quantities worldwide. Most phosphogypsum is stockpiled while lesser quantities are recycled or dumped into water. Phosphogypsum is primarily CaSO4·2H2O, but also contains impurities of environmental concern such as residual acids, fluoride, heavy metals and naturally-occurring radionuclides. Impurity composition within phosphogypsum can vary greatly depending on the source of phosphate rock used in phosphoric acid production. This study was undertaken to obtain detailed information on the composition of phosphogypsum produced from the processing of rock from Florida, Togo and Idaho, to define more clearly the chemical issues of importance to management and use of the by-product. All freshly produced phosphogypsum had sufficiently high fluoride levels that leaching and decomposition of silicate minerals beneath repositories might occur. Phosphogypsum from Idaho rock had elevated Ag, Cd and Se concentrations, and the greate...

Radioactivity and chemical characteristics of Alberta phosphogypsum

Gypsum based by-products of phosphate fertilizer production, termed phosphogypsum (PG), are stockpiled at numerous locations worldwide. Although dominated by gypsum, PG contains accessory minerals, trace elements, and radionuclides. This study was conducted to characterize the composition and pore water chemistry of PG samples from a plant site in southern Alberta, Canada. Pore water chemistry was studied by equilibrating PG with deionized water for 80 days; the aqueous phase was then analyzed for dissolved constituents.The PG samples had pH levels of 4.0 or lower and contained gypsum and minor amounts of quartz, phosphate rock and sodium feldspar. The PG was elevated in total content of Ag, Au, Ca, Cd, P, S, Se, Sr, U and some of the light rare earth elements and Y relative to shale. Average 226Ra activity, determined by the radon emanation method, was 890 Bq kg−1. Activity of 212Pb, in equilibrium with 228Th, was 5.8 Bq kg−1. Pore water concentrations of As, Cd, Cr, Cu, Fe, Mn, Na, NO3−-N, Se, SO42−-S, and Zn exceeded drinking water standards in some PG samples. Although closer to flue gas desulfurization sludge in mineralogy, the pore water chemistry of PG is more like that of some fly ashes.

Effect of glucose amendment on microbial biomass, spelling fertilizer 15N-recovery and distribution in a barley-soil-system

SummaryOne way to conserve fertilizer N in the plant-soil system is to immobilize it at the time of application by adding a readily available C source and to rely on the microorganisms to remineralize it to meet crop N demand during the season. The present study was conducted to determine the effects of microbial activity due to glucose amendment at the time of fertilization and planting on the distribution of fertilizer 15N at harvest among various N pools. Glucose C (150 g m-2) was added to soil at Ellerslie (Black Chernozem) in central Alberta at the time of seeding and fertilization with urea-15N (7.5 g m-2). Barley shoot mass, root mass, and root N at harvest in the non-glucose treatment were 1.8-fold, 1.9-fold, and 2.2-fold greater, respectively, than in the glucose treatment. The recovery of 15N in the soil-plant system was greater in the glucose (82%) than the non-glucose treatment (50%). Likewise, the recovery of 15N in soil was greater in the glucose treatment (72%) than the non-glucose treatment (22%). In both treatments most soil 15N remaining at the time of harvest was present as non-microbial organic 15N, but recovery of 15N in this pool was 3.4-fold greater in glucose-treated than in non-glucose-treated soil. The microbial response to the glucose addition effectively conserved fertilizer N in the active N phase; however, significant remineralization did not occur to meet plant N demands. Microbial transformations in the soil resulted in a constant ratio of non-microbial organic N formed per unit of microbial N formed and this ratio was not affected by the C amendments.

Shoot, root, soil and microbial nitrogen dynamics in two contrasting soils cropped to barley (Hordeum vulgare L.)

SummaryDynamics of barley N, mineral N, and organic N were compared at Ellerslie (Black Chernozem, Typic Cryoboroll) and Breton (Gray Luvisol, Typic Cryoboralf) in central Alberta, using 15N-urea. On average, shoot N and shoot 15N recoveries at Ellerslie (14.1 g m−2, 36%) were greater than at Breton (4.5 g m−2, 17%). Root N (g m−2) did not significantly differ between sites (0–30 cm) but root 15N recovery was greater at Breton (3.4%) than Ellerslie (1.8%). Low levels of shoot N and shoot 15N at Breton were partly due to very wet soil conditions in July, which resulted in premature shoot senescence and low plant N uptake. Although the total 15N recoveries from the system (to 30 cm depth) at Ellerslie (63%) and Breton (56%) were similar, soil 15N was greater at Breton (35%) than at Ellerslie (26%). There were no differences in mineral N between sites but the average 15N recovery in the mineral-N pool was significantly greater at Ellerslie (3.3%) than at Breton (1.6%). There was no difference in 15N recovery in the microbial biomass (∼3%) between sites, although non-microbial organic 15N was greater at Breton (31 %) than at Ellerslie (20%). The two soils showed differences in the relative size of kinetically active N pools and in relative mineralization rates. Microbial N (0–30 cm) was greater at Ellerslie (13.3 g m−2) than at Breton (9.9 g m−2), but total microbial N made up a larger proportion of total soil N at Breton (1.6%) than at Ellerslie (0.9%). In the 0–10 cm interval, microbial N was 1.7-fold greater and non-microbial active N was 3-fold greater at Breton compared to Ellerslie, when expressed as a proportion of total soil N. Net N mineralization in a 10-day laboratory incubation was 1.4-fold greater in the Black Chernozem (0–10 cm interval) from Ellerslie, compared to the Gray Luvisol from Breton, when expressed per gram of soil. Net N mineralization in the soil from Breton was double that of the soil from Ellerslie, when expressed as a proportion of soil N. Although soil N (g m−2) was 2.5-fold greater at Ellerslie compared to Breton, it was cycled more rapidly at Breton.

Slurry-Phase Bioremediation of Creosote and Petroleum-Contaminated Soils

Successful bioremediation often is difficult to achieve because of complex interactions between contaminants, the soil environment, and decomposer organisms. The objective of this work was to study the extent and pattern of contaminant biodegradation during slurry-phase bioremediation of four industrially-contaminated soils (<3% contamination) to obtain further insight into the factors which may control biodegradation. Two soils (sand and silty clay) were contaminated with creosote compounds, and two soils (loam and clay loam) were contaminated with petroleum compounds. Two liter glass jars containing 300g soil and 300ml nutrient solution (300g soil and 100ml nutrient for sand), and 5% inoculum of previously bioremediated soil containing an active culture, were rotated at 3rpm at 22°C in the dark for 10 weeks. Biodegradation was monitored by measuring reductions in total dichloromethane-extractable organics (TEO), selected polycyclic aromatic hydrocarbons (PAHs), and thermal extraction GC-FID detectable c...

Amino acid interference with ammonium determination in soil extracts using the automated indophenol method

Abstract The formation of a colored indophenol complex is commonly used as a quantitative measure of the ammonium content of soil extracts. The potential interference with ammonium determination from co‐extracted amino acids was examined. The extent of color development was examined for 22 amino acids by subjecting pure solutions to ammonium determination by both the indophenol method and steam distillation. Apparent detection of amino acid as ammonium ranged from 0 to 94 % of total nitrogen for the indophenol procedure, whereas steam distillation resulted in little apparent ammonium recovery. With the exception of threonine, the extent of color development was inversely related to amino acid molecular weight. The range in recoveries for the indophenol procedure suggests both size and composition of the co‐extracted amino acid pool is important in determining the extent of interference. Significantly (p=0.001) greater estimates, averaging 0.4 μg mL‐1, were found in indophenol estimates of mineral‐N conten...