Journal Articles

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    Optimal nitrogen fertilizer decisions for rice farming in a cascaded tank system in Sri Lanka: An analysis using an integrated crop, hydro-nutrient and economic model
    (Elsevier B V, 2023-04-01) Kanthilanka H; Ramilan T; Farquharson RJ; Weerahewa J; Timsina J
    CONTEXT: The ancient irrigation systems in Sri Lanka, known as village tank cascade systems, were developed to ensure an adequate and sustainable supply of good quality water to communities. However, there is growing concern about health and environmental issues related to the degradation of water quality caused by excessive nitrogen (N) levels from the overuse of chemical fertilizer. Subsidies for chemical fertilizer have encouraged fertilizer use for rice production in Sri Lanka. OBJECTIVES: The objective was to evaluate the use of N fertilizers for rice production in the Thirappane cascaded tank system and its impact on nitrate water quality. An optimal rate of N use was determined based on private (farm-level) decisions on fertilizer use. However, the private optimal fertilizer rate is not adequate for overall social welfare due to market failures such as incomplete information and the lack of a market to account for the negative impact of fertilizer use on tank water quality. The hypothesis is that the social optimal fertilizer rate is lower than the private optimal rate due to this discrepancy. The study aims to identify the sources of inefficiency in the sub-optimal use of fertilizers from a social perspective. METHOD: We developed an integrated crop, hydro-nutrient and economic model to analyze fertilizer decisions in the rice production process. The method involved conducting a marginal economic analysis based on simulated yield responses to N fertilizer and prices for inputs and outputs. The analysis was performed for three soil types across the Maha (rainy) and Yala (dry) seasons and for three different weather scenarios within each season. RESULTS AND CONCLUSIONS: When the negative impact of nitrate contamination on water quality is taken into account, the optimal N fertilizer rate from a social perspective is always lower than the optimal rate determined solely by private economic considerations. These optimal rates varied based on factors such as soil type, season, weather conditions during the growing season, and fertilizer prices. At unregulated, higher, fertilizer prices, the crop yields achieved at the social optimum were only slightly lower than those achieved under the private economic optimum. However, under regulated, lower, fertilizer prices, achieving the social optimum would require a larger reduction in N fertilizer use and result in a greater decrease in crop yields. SIGNIFICANCE: A systematic analysis that takes into account the social costs can serve as a guide for creating effective policies aimed at enhancing fertilizer decision making
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    Nitrate enrichment does not affect enteropathogenic Escherichia coli in aquatic microcosms but may affect other strains present in aquatic habitats
    (PeerJ, Inc, 2022-09-27) Davis MT; Canning AD; Midwinter AC; Death RG; Oehlmann J
    Eutrophication of the planet's aquatic systems is increasing at an unprecedented rate. In freshwater systems, nitrate-one of the nutrients responsible for eutrophication-is linked to biodiversity losses and ecosystem degradation. One of the main sources of freshwater nitrate pollution in New Zealand is agriculture. New Zealand's pastoral farming system relies heavily on the application of chemical fertilisers. These fertilisers in combination with animal urine, also high in nitrogen, result in high rates of nitrogen leaching into adjacent aquatic systems. In addition to nitrogen, livestock waste commonly carries human and animal enteropathogenic bacteria, many of which can survive in freshwater environments. Two strains of enteropathogenic bacteria found in New Zealand cattle, are K99 and Shiga-toxin producing Escherichia coli (STEC). To better understand the effects of ambient nitrate concentrations in the water column on environmental enteropathogenic bacteria survival, a microcosm experiment with three nitrate-nitrogen concentrations (0, 1, and 3 mg NO3-N /L), two enteropathogenic bacterial strains (STEC O26-human, and K99-animal), and two water types (sterile and containing natural microbiota) was run. Both STEC O26 and K99 reached 500 CFU/10 ml in both water types at all three nitrate concentrations within 24 hours and remained at those levels for the full 91 days of the experiment. Although enteropathogenic strains showed no response to water column nitrate concentrations, the survival of background Escherichia coli, imported as part of the in-stream microbiota did, surviving longer in 1 and 3 mg NO3-N/Lconcentrations (P < 0.001). While further work is needed to fully understand how nitrate enrichment and in-stream microbiota may affect the viability of human and animal pathogens in freshwater systems, it is clear that these two New Zealand strains of STEC O26 and K99 can persist in river water for extended periods alongside some natural microbiota.
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    Exposure to drinking water trihalomethanes and nitrate and the risk of brain tumours in young people
    (Elsevier Inc, 2021-09) Zumel-Marne A; Castaño-Vinyals G; Alguacil J; Villanueva CM; Maule M; Gracia-Lavedan E; Momoli F; Krewski D; Mohipp C; Petridou E; Bouka E; Merletti F; Migliore E; Piro S; Ha M; 't Mannetje A; Eng A; Aragones N; Cardis E
    Brain tumours (BTs) are one of the most frequent tumour types in young people. We explored the association between tap water, exposure to trihalomethanes (THM) and nitrate and neuroepithelial BT risk in young people. Analysis of tap water consumption were based on 321 cases and 919 appendicitis controls (10-24 years old) from 6 of the 14 participating countries in the international MOBI-Kids case-control study (2010-2016). Available historical residential tap water concentrations of THMs and nitrate, available from 3 countries for 86 cases and 352 controls and 85 cases and 343 for nitrate, respectively, were modelled and combined with the study subjects' personal consumption patterns to estimate ingestion and residential exposure levels in the study population (both pre- and postnatal). The mean age of participants was 16.6 years old and 56% were male. The highest levels and widest ranges for THMs were found in Spain (residential and ingested) and Italy and in Korea for nitrate. There was no association between BT and the amount of tap water consumed and the showering/bathing frequency. Odds Ratios (ORs) for BT in relation to both pre- and postnatal residential and ingestion levels of THMs were systematically below 1 (OR = 0.37 (0.08-1.73)) for postnatal average residential THMs higher than 66 μg/L. For nitrate, all ORs were above 1 (OR = 1.80 (0.91-3.55)) for postnatal average residential nitrate levels higher than 8.5 mg/L, with a suggestion of a trend of increased risk of neuroepithelial BTs with increasing residential nitrate levels in tap water, which appeared stronger in early in life. This, to our knowledge, is the first study on this topic in young people. Further research is required to clarify the observed associations.