Do contaminants compromise the use of recycled nutrients in organic agriculture? A review and synthesis of current knowledge on contaminant concentrations, fate in the environment and risk assessment.

Use of nutrients recycled from societal waste streams in agriculture is part of the circular economy, and in line with organic farming principles. Nevertheless, diverse contaminants in waste streams create doubts among organic farmers about potential risks for soil health. Here, we gather the current knowledge on contaminant levels in waste streams and recycled nutrient sources, and discuss associated risks. For potentially toxic elements (PTEs), the input of zinc (Zn) and copper (Cu) from mineral feed supplements remains of concern, while concentrations of PTEs in many waste streams have decreased substantially in Europe. The same applies to organic contaminants, although new chemical groups such as flame retardants are of emerging concern and globally contamination levels differ strongly. Compared to inorganic fertilizers, application of organic fertilizers derived from human or animal feces is associated with an increased risk for environmental dissemination of antibiotic resistance. The risk depends on the quality of the organic fertilizers, which varies between geographical regions, but farmland application of sewage sludge appears to be a safe practice as shown by some studies (e.g. from Sweden). Microplastic concentrations in agricultural soils show a wide spread and our understanding of its toxicity is limited, hampering a sound risk assessment. Methods for assessing public health risks for organic contaminants must include emerging contaminants and potential interactions of multiple compounds. Evidence from long-term field experiments suggests that soils may be more resilient and capable to degrade or stabilize pollutants than often assumed. In view of the need to source nutrients for expanding areas under organic farming, we discuss inputs originating from conventional farms vs. non-agricultural (i.e. societal) inputs. Closing nutrient cycles between agriculture and society is feasible in many cases, without being compromised by contaminants, and should be enhanced, aided by improved source control, waste treatment and sound risk assessments.

Acidification and alkalinization pretreatments of biowastes and their effect on P solubility and dynamics when placed in soil.

BACKGROUND: Sustainability concerns as well as recent increases in fertilizer prices exacerbates the need to optimise the use of biowastes as fertilizers. For this reason, we investigated how different pretreatments affect the P dynamics when biofertilizers are placed in the soil. METHODS: Sewage sludge (SS), sewage sludge ash (SS-ash), meat and bone meal (MBM), and the solid fraction of biogas digestate (BGF) were pretreated with H2SO4, NaOH, and Ca(OH)2 and incubated for 2 and 12 days, respectively, in a one-dimensional reaction system for detailed studies of the interactions in the biomaterial-soil interface and the soil adjacent to the placement zone. RESULTS: Our results showed that acidification and treatment with NaOH increased the P solubility of the biomaterials. The P loss from the biomaterial layer to the soil was correlated with water-extractable P in the biomaterials (0.659) and water-extractable P in the soil (0.809). Acidification significantly increased the total amount of P depleted from the biomaterial to the soil whereas NaOH pre-treatment did not. However, for NaOH-treated SS and SS-ash, the apparent recoveries were significantly higher compared to the acidification due to a decrease in soil P sorption capacity as the soil pH increased due to residual alkalinity in the biomaterials. CONCLUSIONS: Acidification showed promising results by increasing the P solubility of all the biomaterials, and the alkalinization of SS and SS-ash with NaOH by increasing the apparent recovery in the soil. However, further studies are needed to assess the effects of these treatments on plant growth and P uptake.

Reduced turning frequency and delayed poultry manure addition reduces N loss from sugarcane compost.

Composting is an effective method to recycle biodegradable waste as soil amendment in smallholder farming systems. Although all essential plant nutrients are found in compost, a substantial amount of nitrogen is lost during composting. This study therefore investigated the potential of reducing N losses by (i) delaying the addition of nitrogen-rich substrates (i.e. poultry manure), and (ii) reducing the turning frequency during composting. Furthermore, we tested the effect of compost application method on nitrogen mineralization. Sugarcane-waste was composted for 54days with addition of poultry manure at the beginning (i.e. early addition) or after 21days of composting (delayed addition). The compost pile was then turned either every three or nine days. Composts were subsequently applied to soil as (i) homogeneously mixed, or (ii) stratified, and incubated for 28days to test the effect of compost application on nitrogen mineralization. The results showed that delayed addition of poultry manure reduced total nitrogen loss by 33% and increased mineral nitrogen content by >200% compared with early addition. Similarly, less frequent turning reduced total N loss by 12% compared with frequent turning. Stratified placement of compost did not enhance N mineralization compared to a homogeneous mixing. Our results suggested that simple modifications of the composting process (i.e. delayed addition and/or turning frequency) could significantly reduce N losses and improve the plant-nutritional value of compost.

Pulmonary vascular pressures of thoroughbred horses exercised 1, 2, 3 and 4 h after furosemide administration.

Furosemide premedication of horses 4 h prior to exercise significantly attenuates exercise-induced pulmonary capillary hypertension which may help diminish the severity of exercise-induced pulmonary haemorrhage. As pulmonary hemodynamic effects of furosemide may be mediated via a reduction in plasma volume (which is most pronounced 15-30 min postfurosemide administration, with plasma volume recovering thereafter), we hypothesized that administration of furosemide at intervals shorter than 4 h before exertion may be more effective in attenuating the exercise-induced rise in pulmonary capillary blood pressure. Thus, our objective was to determine whether furosemide-induced attenuation of exercise-induced pulmonary arterial, capillary and venous hypertension would be enhanced when the drug is administered at intervals shorter than 4 h before exercise. Using established techniques, right atrial, and pulmonary arterial, capillary and wedge (venous) pressures were ascertained in seven healthy, sound, exercise-trained Thoroughbred horses in a randomized split-plot experimental design. Measurements were made at rest and during exercise performed at maximal heart rate (217 +/- 3 beats/min) in the control (no medications) experiments and following furosemide administration (250 mg intravenously (i.v.)) at 1, 2, 3 and 4 h before exercise. Sequence of treatments was randomized and 7 days were allowed between experiments on each horse. Although furosemide administration in the four treatment groups caused only insignificant changes in the pulmonary arterial, capillary and wedge pressures of standing horses, furosemide-induced reduction in mean right atrial pressure achieved statistical significance in the 2 h postfurosemide experiments. In the control studies, exercise was attended by statistically significant increments in mean right atrial, as well as pulmonary arterial, capillary and wedge pressures. Although exercise in each of the four furosemide experiments was also attended by significant increments in right atrial as well as pulmonary vascular pressures, in the 1, 2 and 3 h postfurosemide experiments, mean right atrial pressure increased to a significantly lower value than in the control study. Exercise-induced changes in pulmonary vascular pressures in the 1 h postfurosemide experiments were not different from the pressures in the control study. There was a significant attenuation of exercise-induced pulmonary capillary and venous hypertension in the 2, 3 and 4 h postfurosemide experiments, but significant differences among these treatments were not found. Thus, these data did not support the contention that administration of furosemide at intervals shorter than 4 h before exercise is more effective in attenuating exercise-induced pulmonary capillary or venous hypertension in Thoroughbred horses.

Short- and long-term survival and prevalence of postoperative ileus after small intestinal surgery in the horse.

The records of 74 horses that recovered from anaesthesia after surgery for a small intestinal lesion from 1994 to 1999 were reviewed. Sixty-three horses (85%) had a strangulating lesion and 43 of these (68%) had a resection and anastomosis. Four of 11 horses (36%) without a strangulating lesion had a resection and anastomosis. Sixty-three horses (85%) survived to discharge, with a survival rate of 53/63 in horses with a strangulating lesion (84%) and 10/11 (91%) in others. For all lesions, short-term survival for all end-to-end anastomoses (91%; 21/23) and for no resection (92%; 23/25) were superior (P < 0.05) to survival for jejunocaecal anastomosis (76%; 19/25). Fourteen horses (19%) had a repeat abdominal surgery during hospitalisation; 9 of these (64%) survived short-term. Postoperative ileus developed in 7/70 horses (10%) after surgery for a problem other than proximal enteritis, and all had a strangulating lesion. Postoperative ileus (POI) was more likely after a jejunocaecostomy than after other procedures, and did not develop after a jejunojejunostomy. Survival > 7 months was 52/69 (75%) and for > 12 months was 39/57 (68%). The estimated prevalence of adhesions was 13%. Short-term survival was poorest in horses that had a jejunocaecostomy, but long-term survival was less affected by the anastomosis used. The sharpest decline in survival was during the first postoperative week and postoperative mortality then declined over time after surgery. A postoperative protocol that allowed early postoperative feeding was well tolerated. The results confirm that the overall prognosis after small intestinal surgery in horses is improved over earlier findings.

Parietal hernia of the small intestine into the epiploic foramen of a horse.

A 12-year old 573-kg (1,261-lb) Quarter Horse gelding was referred with colic of 12 hours' duration and with poor response to medical treatment. On the basis of physical and laboratory findings, a pelvic flexure impaction was suspected. The horse was treated medically. Because signs of mild abdominal pain persisted and the heart rate had increased, an exploratory celiotomy was performed 30 hours after signs of colic were first noticed. At surgery, the ileum was found partially entrapped within the epiploic foramen, in a left-to-right direction, to form a parietal hernia. The entrapped intestinal segment was reduced but not resected, and the horse recovered fully. In retrospect, the delay before surgery in this horse was tolerated because this was a parietal hernia and, therefore, did not cause complete ileal obstruction. This horse had an unusual form of small-intestinal strangulation in the epiploic foramen that might not cause sufficient obstruction initially to allow early detection.

Repeated administration of frusemide does not offer an advantage over single dosing in attenuating exercise-induced pulmonary hypertension in thoroughbred horses.

The objective of the present study was to ascertain whether administration of a second dose of frusemide would attenuate exercise-induced pulmonary hypertension more than a single dose. Right atrial, right ventricular and pulmonary vascular pressures were determined in 7 healthy, sound, exercise-trained Thoroughbred horses at rest and during exercise (14.2 m/s + a 3.5% uphill grade) performed at maximal heart rate (217 +/- 3 beats/min [mean +/- s.e.]). Horses were studied during the following 3 treatments in random order 7 days apart: control (no medication), frusemide single dose (250 mg i.v. 4 h pre-exercise), and frusemide double dose (250 mg i.v., 4 h pre-exercise + 250 mg i.v. 2 h pre-exercise). In the control study, exercise resulted in significant (P < 0.05) right atrial as well as pulmonary arterial, capillary and venous hypertension. In the frusemide single dose experiments, a significant (P < 0.05) attenuation of the exercise-induced rise in right atrial and pulmonary vascular pressures was observed. However, compared with frusemide single dose experiments, significant changes in the exercise-induced right atrial and pulmonary arterial, capillary and venous hypertension were not observed in the frusemide double dose experiments. Therefore, it is concluded that administration of an additional dose of frusemide is unlikely to affect the severity of EIPH in racing Thoroughbred horses more than a single dose.