Journal of Environmental Quality

Phosphorus (P) is an essential element for all life forms. It is a mineral nutrient. Orthophosphate is the only form of P that autotrophs can assimilate. Extracellular enzymes hydrolyze organic forms of P to phosphate. Eutrophication is the overenrichment of receiving waters with mineral nutrients. The results are excessive production of autotrophs, especially algae and cyanobacteria. This high productivity leads to high bacterial populations and high respiration rates, leading to hypoxia or anoxia in poorly mixed bottom waters and at night in surface waters during calm, warm conditions. Low dissolved oxygen causes the loss of aquatic animals and release of many materials normally bound to bottom sediments including various forms of P. This release of P reinforces the eutrophication. Excessive concentrations of P is the most common cause of eutrophication in freshwater lakes, reservoirs, streams, and headwaters of estuarine systems. In the ocean, N becomes the key mineral nutrient controlling primary production. Estuaries and continental shelf waters are a transition zone, where excessive P and N create problems. It is best to measure and regulate total P inputs to whole aquatic ecosystems, but for an easy assay it is best to measure total P concentrations, including paniculate P, in surface waters or N/P atomic ratios in phytoplankton.

The accelerated eutrophication of most freshwaters is limited by P inputs. Nonpoint sources of P in agricultural runoff now contribute a greater portion of freshwater inputs, due to easier identification and recent control of point sources. Although P management is an integral part of profitable agrisystems, continued inputs of fertilizer and manure P in excess of crop requirements have led to a build‐up of soil P levels, which are of environmental rather than agronomic concern, particularly in areas of intensive crop and livestock production. Thus, the main issues facing the establishment of economically and environmentally sound P management systems are the identification of soil P levels that are of environmental concern; targeting specific controls for different water quality objectives within watersheds; and balancing economic with environmental values. In developing effective options, we have brought together agricultural and limnological expertise to prioritize watershed management practices and remedial strategies to mitigate nonpoint‐source impacts of agricultural P. Options include runoff and erosion control and P‐source management, based on eutrophic rather than agronomic considerations. Current soil test P methods may screen soils on which the aquatic bioavailability of P should be estimated. Landowner options to more efficiently utilize manure P include basing application rates on soil vulnerability to P loss in runoff, manure analysis, and programs encouraging manure movement to a greater hectareage. Targeting source areas may be achieved by use of indices to rank soil vulnerability to P loss in runoff and lake sensitivity to P inputs.

Antibiotics are used in animal livestock production for therapeutic treatment of disease and at subtherapeutic levels for growth promotion and improvement of feed efficiency. It is estimated that approximately 75% of antibiotics are not absorbed by animals and are excreted in waste. Antibiotic resistance selection occurs among gastrointestinal bacteria, which are also excreted in manure and stored in waste holding systems. Land application of animal waste is a common disposal method used in the United States and is a means for environmental entry of both antibiotics and genetic resistance determinants. Concerns for bacterial resistance gene selection and dissemination of resistance genes have prompted interest about the concentrations and biological activity of drug residues and break‐down metabolites, and their fate and transport. Fecal bacteria can survive for weeks to months in the environment, depending on species and temperature, however, genetic elements can persist regardless of cell viability. Phylogenetic analyses indicate antibiotic resistance genes have evolved, although some genes have been maintained in bacteria before the modern antibiotic era. Quantitative measurements of drug residues and levels of resistance genes are needed, in addition to understanding the environmental mechanisms of genetic selection, gene acquisition, and the spatiotemporal dynamics of these resistance genes and their bacterial hosts. This review article discusses an accumulation of findings that address aspects of the fate, transport, and persistence of antibiotics and antibiotic resistance genes in natural environments, with emphasis on mechanisms pertaining to soil environments following land application of animal waste effluent.

The literature on pesticide losses in runoff waters from agricultural fields is reviewed. For the majority of commercial pesticides, total losses are 0.5% or less of the amounts applied, unless severe rainfall conditions occur within 1–2 weeks after application. Exceptions are the organochlorine insecticides, which may lose about 1% regardless of weather pattern because of their long persistence; and soil surface‐applied, wettable‐powder formulations of herbicides, which may lose up to 5%, depending on weather and slope, because of the ease of washoff of the powder.

Pesticides with solubilities of 10 ppm or higher are lost mainly in the water phase of runoff, and erosion control practices will have little effect on such losses. Organochlorine pesticides, paraquat, and arsenical pesticides, however, are important cases of pesticides which are strongly adsorbed by sediments, and erosion control can be important in controlling losses of these compounds.

The behavior and fate of pesticides in streams receiving runoff is generally not known. Information on such factors as time and distance of impact of a given runoff event, ability of local ecosystems to recover from transient pesticide concentrations, and dissipation or concentration processes in aquatic ecosystems will have to be obtained before “edge‐of‐field” pesticide losses can be related to water quality in receiving waters.

Một thí nghiệm trong chậu được thực hiện để so sánh hai chiến lược xử lý ô nhiễm bằng thực vật: tích tụ tự nhiên sử dụng thực vật siêu tích tụ Zn và Cd là Thlaspi caerulescens J. Presl & C. Presl so với chiết xuất cải tiến hóa học sử dụng ngô (Zea mays L.) được xử lý bằng axit ethylenediaminetetraacetic acid (EDTA). Nghiên cứu sử dụng đất bị ô nhiễm công nghiệp và đất nông nghiệp bị ô nhiễm kim loại từ bùn thải. Ba vụ mùa của T. caerulescens trồng trong vòng 391 ngày đã loại bỏ hơn 8 mg kg⁻¹ Cd và 200 mg kg⁻¹ Zn từ đất bị ô nhiễm công nghiệp, tương đương 43% và 7% các kim loại trong đất. Ngược lại, nồng độ Cu cao trong đất nông nghiệp đã làm giảm nghiêm trọng sự phát triển của T. caerulescens, do đó hạn chế tiềm năng chiết xuất của nó. Quá trình xử lý bằng EDTA đã tăng đáng kể tính hòa tan của kim loại nặng trong cả hai loại đất, nhưng không dẫn đến tăng lớn hàm lượng kim loại trong chồi ngô. Chiết xuất Cd và Zn bằng ngô + EDTA nhỏ hơn nhiều so với T. caerulescens từ đất bị ô nhiễm công nghiệp, và nhỏ hơn (Cd) hoặc tương tự (Zn) so với đất nông nghiệp. Sau khi xử lý bằng EDTA, kim loại nặng hòa tan trong nước lỗ chân lông của đất chủ yếu tồn tại dưới dạng phức hợp EDTA-kim loại, duy trì trong vài tuần. Hàm lượng cao của kim loại nặng trong nước lỗ chân lông sau quá trình xử lý EDTA có thể gây nguy cơ môi trường dưới dạng ô nhiễm nước ngầm.

Antibiotics are commonly added to animal feed as supplements to promote growth of food animals. However, absorption of antibiotics in the animal gut is not complete and as a result substantial amounts of antibiotics are excreted in urine and feces that end up in manure. Manure is used worldwide not only as a source of plant nutrients but also as a source of organic matter to improve soil quality especially in organic and sustainable agriculture. Greenhouse studies were conducted to determine whether or not plants grown in manure‐applied soil absorb antibiotics present in manure. The test crops were corn (Zea maysL.), green onion (Allium cepaL.), and cabbage (Brassica oleraceaL. Capitata group). All three crops absorbed chlortetracycline but not tylosin. The concentrations of chlortetracycline in plant tissues were small (2–17 ng g⁻¹fresh weight), but these concentrations increased with increasing amount of antibiotics present in the manure. This study points out the potential human health risks associated with consumption of fresh vegetables grown in soil amended with antibiotic laden manures. The risks may be higher for people who are allergic to antibiotics and there is also the possibility of enhanced antimicrobial resistance as a result of human consumption of these vegetables.

Because reduced Cr has been considered to be the stable form in soils, we were surprised to find that added trivalent Cr oxidizes readily to the hexavalent form under conditions prevalent in many field soils. The key to the oxidation appears to be the presence in the soil of oxidized Mn, which serves as the electron acceptor in the reaction. The relative ability of a soil to oxidize Cr may be predicted by measuring Mn reducible by hydroquinone, or it may be determined directly by means of a quick test in which Cr(III) is added to a fresh moist soil sample.

Oxidation of Cr by soils was not discovered earlier because the importance of studying fresh field soils, rather than crushed, dried, stored samples, was not appreciated. Plants were severely damaged by Cr(VI) formed from Cr(III) added to fresh soil samples. Hexavalent Cr still was present in a soil stored moist at 25°C for 5 mo.

The sustainable management of fertilizer and manure P to minimize freshwater eutrophication requires identification of soil P levels that exceed crop P requirements and have the potential for P enrichment of runoff. Although several states have established such P levels, insufficient data are available to theoretically justify them. Thus, this study investigates the relationship between the concentrations of P in runoff and in soil. Surface samples (0–10 cm) of 10 Oklahoma soils were packed in 0.15 m² boxes, incubated for 7 d with poultry litter (0–20 Mg ha⁻¹) to obtain a range in Mehlich‐3 P contents (7–360 mg kg⁻¹), and received five 30‐min rainfalls applied at 1‐d intervals. The concentration of dissolved, bioavailable, and particulate P in runoff was related (r² > 0.90; P < 0.1) to the Mehlich‐3 P content of surface soil (0–1 cm), with regression slopes ranging from 2.0 to 7.2, increasing as soil P sorption maxima increased (r² = 0.93). Two soils of 200 mg kg⁻¹ Mehlich‐3 P supported a dissolved P concentration in runoff of 280 μg L⁻¹ (San Saba clay; fine, montmorillonitic, thermic Udic Pellustert) and 1360 μg L⁻¹ (Stigler silt loam; fine, mixed, thermic Aquic Paleudalf). Thus, relationships between runoff and soil P will have to be soil specific for use in management recommendations. A single linear relationship described the dependence of dissolved (r² = 0.86) and bioavailable P (r² = 0.85) on soil P sorption saturation. The added complexity of the P saturation approach may limit its application; however, the approach integrates the effect of soil type with soil P content to better estimate the potential for P loss in runoff than soil P alone.