Transformation Of Organic Phosphorus Research Articles

Molecular insights into effects of chemical conditioning on dissolved organic phosphorus transformation and bioavailability during sludge composting

Phosphorus is enriched in waste activated sludge (WAS) during wastewater treatment, and organic phosphorus (OP) is a potential slow-release P fertilizer. The chemical coagulants used in sludge dewatering leave numerous residues in WAS that affect sludge composting. In this study, the effects of polyaluminum chloride (PAC) and polyferric sulfate (PFS) on the bioconversion of dissolved OP (DOP) during sludge composting were investigated. The results revealed that PFS conditioning promoted the transformation and bioavailability of DOP, whereas PAC conditioning inhibited. Results indicated that PFS conditioning enhanced the transformation of OP molecules in the thermophilic phase. Through oxidation and dehydrogenation reactions, 1-hydroxy-pentane-3,4-diol-5-phosphate and D-ribofuranose 5-phosphate with high bioactivity were generated in the PFS-conditioned compost. Enzymatic hydrolysis experiments further verified that PFS conditioning enhanced the DOP bioavailability in the compost, whereas PAC conditioning inhibited it. The study has provided molecular insights into the effects of chemical conditioning on DOP conversion during sludge composting.

Introducing N2-fixing tree species into Eucalyptus plantations increases organic phosphorus transformation but decreases its accumulation within aggregates in subtropical China

Introducing N2-fixing tree species into Eucalyptus plantations increases organic phosphorus transformation but decreases its accumulation within aggregates in subtropical China

Dissolved organic carbon spurs bacterial-algal competition and phosphorus-paucity adaptation: Boosting Microcystis' phosphorus uptake capacity

Dissolved organic carbon (DOC) can alter the availability of background nutrients by affecting the proliferation of heterotrophic bacteria, which exerts a notable influence on algal growth and metabolism. However, the mechanism of how allochthonous DOC (aDOC) precipitates shifts in bacterial-algal interactions and modulates the occurrence of cyanobacteria blooms remains inadequately elucidated. Therefore, this study investigated the relationship between bacteria and algae under aDOC stimulation. We found that excess aDOC triggered the breakdown and reestablishment of the equilibrium between Microcystis and heterotrophic bacteria. The rapid proliferation of heterotrophic bacteria led to a dramatic decrease in soluble phosphorus and thereby resulted in the inhibition of the Microcystis growth. When the available DOC was depleted, the rapid death of heterotrophic bacteria released large amounts of dissolved phosphorus, which provided sufficient nutrients for the recovery of Microcystis. Notably, Microcystis rejuvenated and showed higher cell density compared to the carbon-absent group. This phenomenon can be ascribed that Microcystis regulated the compositions of extracellular polymeric substances (EPS) and the expression of relevant proteins to adapt to a nutrient-limited environment. Using time of flight secondary ion mass spectrometry (TOF-SIM) and proteomic analysis, we observed an enhancement of the signal of organic matter and metal ions associated with P complexation in EPS. Moreover, Microcystis upregulated proteins related to organic phosphorus transformation to increase the availability of phosphorus in various forms. In summary, this study emphasized the role of DOC in algal blooms, revealing the underestimated enhancement of Microcystis nutrient utilization through DOC-induced heterotrophic competition and providing valuable insights into eutrophication management and control.

Mechanism of organic phosphorus transformation and its impact on the primary production in a deep oligotrophic plateau lake during stratification

Global warming is leading to extended stratification in deep lakes, which may exacerbate phosphorus (P) limitation in the upper waters. Conversion of labile dissolved organic P (DOP) is a possible adaptive strategy to maintain primary production. To test this, the spatiotemporal distributions of various soluble P fractions and phosphomonesterase (PME)/phosphodiesterase (PDE) activities were investigated in Lake Fuxian during the stratification period and the transition capacity of organic P and its impact on primary productivity were evaluated. The results indicated that the DOP concentration (mean 0.20 ± 0.05 μmol L−1) was significantly higher than that of dissolved inorganic P (DIP) (mean 0.08 ± 0.03 μmol L−1) in the epilimnion and metalimnion, which were predominantly composed of orthophosphate monoester (monoester-P) and orthophosphate diesters (diester-P). The low ratio of diester-P / monoester-P and high activities of PME and PDE indicate DOP mineralization in the epilimnion and metalimnion. We detected a DIP threshold of approximately 0.19 μmol L−1, corresponding to the highest total PME activity in the lake. Meta-analysis further demonstrated that DIP thresholds of PME activities were prevalent in oligotrophic (0.19 μmol L−1) and mesotrophic (0.74 μmol L−1) inland waters. In contrast to the phosphate-sensitive phosphatase PME, dissolved PDE was expressed independent of phosphate availability and its activity invariably correlated with chlorophyll a, suggesting the involvement of phytoplankton in DOP utilization. This study provides important field evidence for the DOP transformation processes and the strategy for maintaining primary productivity in P-deficient scenarios, which contributes to the understanding of P cycles and the mechanisms of system adaptation to future long-term P limitations in stratified waters.

Spectroscopic Investigation of Phosphorus Mineralization as Affected by the Calcite-Water Interfacial Chemistry.

The mineralization and bioavailability of phytic acid, the predominant organic phosphorus (OP) species in many soils, have generally been rendered limited due to its interaction with soil minerals. In particularly calcareous and neutral to slightly alkaline soils, phytic acid is known to actively react with calcite, although how this interaction affects phytic acid mineralization is still unknown. This study, therefore, investigated the mechanisms regarding how the calcite-water interface influences phytic acid mineralization by phytase, at pHs 6 and 8 using in situ spectroscopic techniques including solution nuclear magnetic resonance and attenuated total reflection Fourier transform infrared spectroscopy. The findings indicated a pH-specific effect of the calcite-water interface. Inhibited phytase activity and thus impaired phytic acid mineralization were induced by calcite at pH 6, while the opposite effect was observed at pH 8. How the interaction between phytic acid and calcite and between phytase and calcite differed between the two pH values contributed to the pH-specific effect. The results demonstrate the importance of soil pH, enzyme-, and OP-clay mineral interactions in controlling the mineralization and transformation of OP and, consequently, the release of phosphate in soils. The findings can also provide implications for the management of calcite-rich and limed soils.

Post-agricultural succession affects the accumulation and enzymatic transformation of organic phosphorus in a karst area, southwest China

Post-agricultural succession affects the accumulation and enzymatic transformation of organic phosphorus in a karst area, southwest China

Hydrophyte Debris Induced Sedimentary Phosphorus Release in Tuojiang Rivers, China.

Hydrophyte debris decomposition may contribute to phosphorus (P) release from the sediments in riverine systems, but the transport and transformation of organic phosphorus during this process has not been studied well. Here, a ubiquitous hydrophyte in southern China (Alternanthera philoxeroides, A. philoxeroides) was selected to identify the processes and mechanisms of sedimentary P release in late autumn or early spring by laboratory incubation. The results showed that the physio-chemical interactions changed quickly during the beginning of the incubation, where the redox potential and dissolved oxygen at the water-sediment interface decreased rapidly, reaching reducing (299 mV) and anoxic (0.23mg∙L-1) conditions, respectively. Soluble reactive P, dissolved total P and total P concentrations in overlying water all increased with time from 0.011, 0.025 and 0.169mg∙L-1 to 0.100, 0.100 and 0.342mg∙L-1 on average, respectively. Furthermore, the decomposition of A. philoxeroides induced sedimentary organic P release to overlying water, including phosphate monoester (Mono-P), and orthophosphate diesters (Diesters-P). The proportions of Mono-P and Diesters-P were higher at 3 to 9 days than at 11 to 34 days, being 29.4% and 23.3 for Mono-P, 6.3% and 5.7% for Diesters-P, respectively. Orthophosphate (Ortho-P) increased from 63.6 to 69.7% during these timeframes, which indicated the transformations of both Mono-P and Diester-P to bio-available orthophosphate (Ortho-P), causing the rising P concentration in the overlying water. Our results revealed that hydrophyte debris decomposition in river systems might lead to autochthonous P contribution even without external P import from the watershed, accelerating the trophic state of receiving waterbodies.

Distribution and Release Potential of Soil Phosphorus Fractions in Water-level Fluctuation Zone of the Tributary Bay, Three Gorges Reservoir

After repeated wetting-drying cycles, the migration and transformation of phosphorus in the water-level fluctuation zone (WLFZ) are accelerated, and the eutrophication of tributary bays in the reservoir becomes increasingly serious. Soils in the WLFZ of a typical tributary of the Three Gorges Reservoir were collected, and then phosphorus forms and the degree of phosphorus saturation (DPS) were determined to analyze the phosphorus release potential. The results showed that, ① the average contents of total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) of soils in the WLFZ were 771.80, 485.33, and 166.30 mg·kg-1, respectively. The non-labile IP and OP were the dominate speciation of IP and OP, respectively. ② The distribution of P forms of soils in the WLFZ was affected by wetting-drying cycle. The contents of Ex-P and NaHCO3-Po of soils in the WLFZ were significantly higher than those in the contrasted soils, whereas the contents of Fe-P, HCl-Po, and Fulvic-Po decreased significantly along the elevation (P<0.05). The alternative wetting-drying cycle promoted the generation of labile P and the release and accumulation of moderately labile P of soils in the WLFZ. ③The content and proportion of bioavailable phosphorus (Bio-P) of soils in the WLFZ were in the range of 49.19-148.78 mg·kg-1 and 7.17%-24.78%, and the degree of phosphorus sorption (DPS) was in the range of 5.85%-22.00%. At present, the phosphorus release risk of soils in the WLFZ was low. The soil at 170 m elevation requires further attention. Fe-P, HCl-Po, and Fulvic-Po contributed significantly to phosphorus release. The increase in pH promoted the release of Fe-P. Alkaline phosphomonoesterase (ALP) was an important participant in the transformation of OP. Additionally, organic matter (OM) was the main source of OP.

Characteristics and controls of inorganic and organic phosphorus transformation during long-term paddy soil evolution

Information on phosphorus (P) transformation during long-term paddy soil evolution is important for maintaining rice yield and nutrient management. This study was aimed to reveal the characteristics and controls of inorganic and organic P transformation during paddy soil evolution over a millennial time scale using both sequential chemical extraction and solution 31P nuclear magnetic resonance spectroscopy. Results show that the rate and trajectory of P evolution in the topsoil differ markedly from that of the illuvial horizon. The amount of apatite P, non-occluded P, occluded P and total P in the topsoils increased rapidly during the early stage of paddy soil evolution (< 50 yrs) due to anthropogenic P additions, but declined in the older paddy soils due to the leaching loss of P sorbents (CaCO3 and Fe/Al oxides); thus, the added P cannot be efficiently retained by the older paddy soils. Total organic P including phosphate monoester in the topsoils reached maximum in the 300-yr paddy soil and declined thereafter. However, the phosphate diester pool (including DNA) and its proportion in the topsoil increased continuously across the paddy soil chronosequence, suggesting that long-term paddy cultivation promoted labile organic P accumulation. In the deeper soil horizons with less human impacts, the temporal trends in inorganic and organic P across the paddy soil chronosequence can be fully predicted by previous established P transformation models during natural pedogenesis, although the rates of P changes differ among different sites. Our study demonstrates that long-term paddy cultivation alters the rate and trajectory of inorganic and organic P transformation in the topsoils over a millennial time scale, and highlights the importance of labile organic P activation for nutrient supply in the older paddy soils.

The effect of iron oxide types on the photochemical transformation of organic phosphorus in water

Iron oxides play an important role in the transport and transformation of organic phosphorus in aquatic environments. However, the effect of different types of iron oxide on the environmental fate of organic phosphorus has remained unclear. In this study, the photodegradation of the organic phosphorus compound adenosine triphosphate (ATP) via the activity of crystalline (goethite) and amorphous (ferrihydrite) iron oxides was investigated. It was found that ATP was photodegraded by goethite, resulting in the release of dissolved inorganic phosphate under simulated sunlight irradiation. The concentration of ATP on goethite decreased by 75% after 6 h of simulated sunlight irradiation, while the concentration of ATP on ferrihydrite decreased by only 22%. ATR-FTIR spectroscopy revealed that the intensity of the peaks for the P–O and PO stretching vibrations in the goethite−ATP complex decreased significantly more after simulated sunlight irradiation than did those for the ferrihydrite treatment. Combined with the higher TOC/TOC0 values for the goethite treatment, the results indicate that a more vigorous photochemical reaction took place in the presence of goethite than with ferrihydrite. Reactive oxygen species analysis also showed that hydroxyl and superoxide anion radicals were generated when goethite was exposed to simulated sunlight irradiation, while ferrihydrite did not exhibit this ability. Overall, this study highlights that the type of iron oxide is an important factor in the transformation of organic phosphorus in aquatic environments.

Response of organic phosphorus in lake water to environmental factors: A simulative study

Transformation of organic phosphorus (P) is directly related to a range of environmental factors, therefore exploring their relationships is vital to understanding the biogeochemical cycling of P and its significance in eutrophication of lake waters. In this study, a series of experiments were conducted to simulate the organic P transformation in the water under the influence of dissolved oxygen (DO), temperature and phytoplankton growth. Results showed that the transformation rate of total organic P increased with temperature, ranging from 0.02 to 0.25 mg L−1 day−1 at 5 °C, and from 0.04 to 0.72 mg L−1 day−1at 30 °C. The transformation rate of total organic P was significantly higher under anaerobic conditions than that under aerobic conditions at 20 °C and 30 °C, indicating that DO is a more important factor for the transformation of total organic P at the high temperature. However, different compounds of organic P responded differently to environmental factors. The change of orthophosphate monoester (Mono-P) content was consistent with that of total organic P when the temperature and DO were the same, but the transformation rates of phosphonate and DNA in the water were less affected by changes of temperature and DO. Additionally, the transformation rate of Mono-P was increased by the growth of phytoplankton when it was used as a P source. Although the relationships between alkaline phosphatase (ALP) activity and organic P are complex, ALP may be the main factor affecting the transformation of organic P at lower temperatures.

Characteristics and Controls of Inorganic and Organic Phosphorus Transformation in a Chinese Subtropical Paddy Soil Chronosequence

Characteristics and Controls of Inorganic and Organic Phosphorus Transformation in a Chinese Subtropical Paddy Soil Chronosequence

First attempt for in situ capping with lanthanum modified bentonite (LMB) on the immobilization and transformation of organic phosphorus at the sediment-water interface

LMB is a widely utilized material for the management of sediment-derived phosphorus (P) in eutrophic lakes. However, the properties of organic P at the sediment-water interface and the effect of LMB on organic P fractions in sediments are still unclear. The batch studies reported here indicate that LMB has good adsorption properties toward organic P (Glucose-6-phosphate), and the tentative adsorption mechanism relies on chemisorption. Laboratory microcosmic experiments were conducted to study the immobilization effect of LMB on the organic P in water and sediments. The results indicated that the concentration of total P, labile P and organic P in overlying water and pore water could be effectively reduced by LMB capping of sediments. After treatment, the optimal immobilization effects appeared on the 7th day and until the 60th day. However, the fractions of organic P change during the capping time. Active organic P eluted with NaHCO3 transforms into moderately labile or non-labile P through the physical and chemical processes, as well as microbial action. Microbial community analysis showed that the addition of LMB had inhibitory effect on the phosphorus-solubilizing bacteria, which also affected the transformation between various forms of organic P. This study provided new insights of LMB in situ capping of organic P and the mechanisms of the migration and cycling of internal organic P, which is beneficial for the management of eutrophic lakes.

Composition characterization and biotransformation of dissolved, particulate and algae organic phosphorus in eutrophic lakes

Characteristics and transformation of organic phosphorus in water are vital to biogeochemical cycling of phosphorus and support of blooms of phytoplankton and cyanobacteria. Using solution 31P nuclear magnetic resonance (NMR), combined with field surveys and lab analyses, composition and structural characteristics of dissolved phosphorus (DP), particulate phosphorus (PP) and organic P in algae were studied in two eutrophic lakes in China, Tai Lake and Chao Lake. Factors influencing migration and transformation of these constituents in lake ecosystems were also investigated. A method was developed to extract, flocculate and concentrate DP and PP from lake water samples. Results showed that orthophosphate (Ortho-P) constituted 32.4%–81.3% of DP and 43.7%–54.9% of PP, respectively; while monoester phosphorus (Mono-P) was 13.2%–54.0% of DP and 32.9%–43.7% of PP, respectively. Phosphorus in algae was mostly organic P, especially Mono-P, which was ≥50% of TP. Environmental factors and water quality parameters such as temperature (T), electrical conductivity (EC), pH, secchi depth (SD), dissolved oxygen (DO), chemical oxygen demand (CODcr), chlorophyll-a (Chl-a), affected the absolute and relative concentrations of various P components in the two lakes. Increased temperature promoted bioavailable P (Ortho-P and Mono-P) release to the lake waters. The results can provide an important theoretical basis for the mutual conversion process of organic P components between various media in the lake water environment.

Effects of exogenous spermidine and arbuscular mycorrhizal fungi on plant growth of cucumber

Effects of spermidine (Spd) and arbuscular mycorrhizal fungi (AMF) on the growth and photosynthesis of cucumber (Cucumis sativus L., cv. Jinchun 2) seedlings, fruit yield and quality, microorganism and enzymatic activity in rhizosphere were investigated. The results showed that combined Spd and AMF addition significantly promoted the growth of cucumber seedlings, increased the root activity, fruit production and quality, enhanced nutrients absorption of seedlings. Net photosynthetic rate, actual photochemical efficiency, light quantum efficiency, carboxylation efficiency and light respiration rate of cucumber seedlings were increased by combined addition of Spd and AMF. The abundance of bacteria and actinomycetes in the rhizosphere of cucumber seedlings were increased, but that of fungi was decreased. The activities of enzymes, including sucrase, neutral phosphatase, catalase, and urease, were enhanced. These results suggested that the light utilization efficiency of cucumber seedlings was improved by combined addition of Spd and AMF. The growth substrate has been changed from a low-fertility type caused by fungi to a high-fertility one caused by bacteria. The decomposition and transformation of organic phosphorus and nitrogen in substrate were increased by combined addition of Spd and AMF, and thus could provide more N and P for the growth and development of cucumber, which further led to enhanced seedling growth, higher yield and quality of fruits. Moreover, Spd could increase the infection rate of AMF in cucumber roots, and together they had a synergistic effect on the growth of cucumber. Our results suggest that it is an effective method to enhance the infection rate of AMF by using Spd.

Nutrient addition affects net and gross mineralization of phosphorus in the organic layer of a tropical montane forest

In tropical ecosystems with highly weathered soils, transformation of organic phosphorus (P) to bioavailable inorganic P plays a crucial role for the nutrition of organisms. In these ecosystems, P is suspected to be growth-limiting and might therefore be affected by atmospheric nutrient deposition occurring even in remote areas such as montane rainforests. We assessed effects of P and nitrogen (N) addition on net and gross P mineralization rates, and microbial P immobilization in the organic layer along an altitudinal gradient of a tropical montane rainforest in Ecuador. Net P mineralization rates amounted to 1.8 ± 0.9 (at 1000 m a.s.l.), 3.7 ± 0.6 (at 2000 m) and 2.0 ± 0.4 (at 3000 m) mg P kg−1 day−1. Altitudinal differences led to an increased microbial P immobilization at 1000 m compensating for a higher gross P mineralization. P addition increased net P mineralization rates at 2000 and 3000 m, suggesting a higher P demand at 1000 m. At higher altitudes, P likely was released as a by-product during organic matter decomposition. Gross P mineralization, determined by means of the isotopic dilution approach, could not be calculated for control and N treatments due to rapid microbial P immobilization. For P (+N) treatments, gross P mineralization rates were lowest at the 1000 m site towards the end of the long-term incubation period. Atmospheric P deposition in the tropics might lead to P fertilization effects through direct input as well as through acceleration of P release from organic matter, thereby increasing P availability for organisms.

Fractions and transformation of organic phosphorus in sediments from a eutrophic lake in China

Several organic phosphorus compounds (Po) in sediment from a representative eutrophic lake were surveyed using a sequential fractionation procedure, which included microbial biomass phosphorus (Biomass-P), fulvic acid phosphorus (FA-P), humic acid phosphorus (HU-P), and residual phosphorus (Res-P). In addition, several organic compounds including orthophosphate monoesters, orthophosphate diesters, and pyrophosphate were simultaneously measured using 31P nuclear magnetic resonance (31P NMR). Results showed that Po contributed over 50% of total phosphorus (TP), and the average concentration of Po species generally decreased from Res-P>FA-P>HU-P>Biomass-P. Additionally, the relative proportions of phosphorus compounds in the sediment followed the decreasing order of orthophosphate monoesters > orthophosphate diesters > pyrophosphate. In general, Po was the dominant phosphorus species. Residual P was not a single species but comprised of a group of species, and tended to be stable. Although orthophosphate monoesters had the highest concentrations and ratios in Po, orthophosphate diesters displayed a more distinct remineralization trend. Principal component analysis (PCA) coupled with correlation analysis suggested that a greater amount of orthophosphate diesters resided in Res-P, than HU-P or FA-P.

Soil organic phosphorus transformations during 2000 years of paddy-rice and non-paddy management in the Yangtze River Delta, China

The contents and properties of soil organic phosphorus (Po) largely drive ecosystem productivity with increasing development of natural soil. We hypothesized that soil Po would initially increase with paddy management and then would persist under steady-state conditions. We analyzed soils from a 2000-year chronosequence of a rice-wheat rotation and an adjacent non-paddy 700-year chronosequence in Bay of Hangzhou (China) for their Po composition using solution 31P-NMR after NaOH-EDTA extraction. Land reclamation promoted Po accumulation in both paddy and non-paddy topsoils (depths ≤ 18 cm) until steady-state equilibria were reached within 200 years of land use. Greater Po concentrations were found, however, in the non-paddy subsoils than in those under paddy management. Apparently, the formation of a dense paddy plough pan hindered long-term Po accumulation in the paddy subsoil. The surface soils showed higher proportions of orthophosphate diesters under paddy than under non-paddy management, likely reflecting suppressed decomposition of crop residues despite elevated microbial P compounds stocks under anaerobic paddy-rice management. Intriguingly, the composition of Po was remarkably stable after 194-years of paddy management and 144-years of non-paddy management, suggesting novel steady-state equilibria of P dynamics had been reached in these man-made ecosystems after less than two centuries.

Soil organic phosphorus transformation during ecosystem development: A review

Soil organic phosphorus transformation during ecosystem development exerts a crucial influence on soil fertility and ecosystem properties. This paper reviews the use of solution 31P NMR spectroscopy for characterizing organic phosphorus speciation in soil chronosequence and long-term field experiments in order to improve our understanding of the temporal changes, fundamental processes, and associated natural and anthropogenic controls of organic phosphorus transformation during long-term ecosystem evolution. Published soil chronosequence studies show that organic phosphorus compounds under aerobic conditions are dominated by phosphate monoesters (occurred mainly as inositol phosphates) followed by phosphate diesters (occurred mainly as DNA) and phosphonates, irrespective of the different parent materials, vegetation covers and climatic conditions. This contrasted markedly with wetland soils in which phosphate monoesters and diesters maintained approximately equal proportions, which is attributed to the limited reactive clay surfaces for stabilization and/or decomposition of myo-inositol hexakisphosphate under frequent anaerobic conditions. Most organic phosphorus compounds in soil chronosequences increase with age to reach a maximum and then decline with time, although the apex varies significantly among different organic phosphorus compounds and chronosequences. Variations of the potential for phosphorus stabilization resulting from mineralogical transformation, changes in phosphorus sources due to shifts in plant and microbial communities, and differences in the biological utilization of various phosphorus compounds have been suggested as three main mechanisms controlling the temporal changes in organic phosphorus species, abundance and availability during natural ecosystem development. In agricultural soils, the amounts, forms, and dynamics of organic phosphorus are determined by internal soil properties, external environmental conditions and managements, including the history and intensity of land use, different tillage practices and fertilizer treatments. These mechanisms are interlinked and more research is required to isolate both internal and external factors that regulate organic phosphorus transformation in agricultural ecosystems. Given the universal dependence on organic phosphorus for life and its critical roles in biogeochemical cycling, we put forward several open questions that need to be resolved in the future studies by emphasizing the multidisciplinary collaborations, the use of multiple analytical techniques and the establishment of quantitative organic phosphorus transformation models.

Photodecomposition of organic phosphorus in aquatic solution under solar irradiation with nitrate: Kinetics and influencing water parameters

The transformation of organic phosphorus plays an important role in the phosphorus cycle in the natural environment. In this study, a series of laboratory‐based experiments were conducted to address the influence of nitrate ( ) photochemical activity on the transformation of methyl parathion under solar irradiation. It is demonstrated that the photodecomposition of methyl parathion by obeys pseudo‐first‐order reaction kinetics, with the photodecomposition rate increasing with concentration. The photodecomposition rates of methyl parathion by were strongly influenced by pH, concentration of humic acid and Fe3+. Higher concentrations of Fe3+ and lower concentrations of humic acid accelerated the photodegradation induced by . Moreover, compared to alkaline media the acidic media can enhance the rate of methyl parathion degradation. Formation of the hydroxyl radical (•OH) was identified through the measurement of photoluminescence spectra (PL) using terephthalic acid as the trapping molecule. The primary transformation pathways of methyl parathion in the presence of under solar irradiation were proposed through the qualitative and quantitative analysis of byproducts. Intermediates, such as paraoxon, 4‐nitrophenol and orthophosphate, were identified, and a mineralization pathway from methyl parathion to orthophosphate was proposed. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 404–411, 2017