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Pesticide use in developing countries such as the Philippines has significantly increased food production. However, the improper and poorly regulated practice of pesticide use may lead to pollution of water resources. To detect and assess the extent of pesticide contamination, residues of organochlorine pesticides were tested in surface water and groundwater in selected areas along the Pampanga River, Philippines. The physicochemical properties of the surface water and ground water were also analyzed and results revealed that phosphate concentrations in surface water and groundwater samples were two to three times higher than the regulatory limits of 0.5 mg L −1 , whereas the nitrate concentrations were below the regulatory limit of 7 mg L −1 . Results further revealed that surface water and groundwater showed the presence of seven organochlorine pesticides and residues listed in the Stockholm Convention list of 2009 such as dieldrin, endrin aldehyde, α-BHC, β-BHC, δ-BHC, γ-chlordane, and endosulfan II. The concentrations of organochlorine pesticides including endrin aldehyde, total BHCs (i.e., α-BHC, β-BHC, δ-BHC), and heptachlor in groundwater were also found to exceed regulatory limits, indicating that these chemicals are still being used illegally and remains a major environmental concern despite the bans and restrictions. We suggest that routine chemical monitoring (including seasonal variations) coupled with biological monitoring using a battery of biomarker tests of organochlorine pesticide and residues along the Pampanga River is necessary to provide inputs for the control and reduction of environmental pollution and for minimizing human health risks.

The natural abundance of Cr and Ni in serpentine soils is well-known, but the food safety of rice grown in these hazardous paddy soils is poorly understood. The study evaluated the bioaccumulation of chromium (Cr) and nickel (Ni) in rice ( Oryza sativa ) grown in serpentine-derived paddy soils in the Philippines. Surface soil (0–20 cm) samples were collected and characterized across three (i.e., Masinloc, Candelaria, and Sta. Cruz) paddy areas in Luzon Island, Philippines. At least 3 to 4 whole rice plants at mature stage were uprooted manually in each sampling point where the soil samples were collected. The total Cr and Ni concentrations in rice (i.e., roots, shoots, and grains) and soil, soil physicochemical properties, bioaccumulation factor (BAF), translocation factor (TF), and the hazard quotients (HQ) were determined. Results revealed that Cr and Ni in rice were accumulated mostly in the roots. Although paddy soils had elevated total Cr and Ni concentrations, the BAF and soil-to-root TF values for Cr and Ni were < 1. In terms of human health risks, results further revealed low risk for both male and female Filipino adults as HQ values for Cr and Ni were < 1. While it is safe to consume rice grown in the area in terms of Cr and Ni dietary intake, more studies are necessary to understand the dynamics and bioavailability of these heavy metals in other crops and drinking water from tube wells in these areas in order to provide a more holistic human health-based assessments and to ensure consumer safety in serpentine areas. In addition, a more reliable data on Cr and Ni speciation in serpentine soils and crops is critically important. Further studies are also needed to understand the contribution of bioavailable heavy metals in improving the soil health to achieve food safety.

To elucidate the dynamics of mercury emitted and released by artisanal and small-scale gold mining (ASGM) activity and to estimate its impact on the ecosystems of the bay, the distribution of mercury in the atmosphere, soil, water, and sediment around Mambulao Bay, Camarines Norte, Philippines, was investigated. The ASGM operations use mercury to extract gold from ore and are located on the east shore side of the bay. Samplings were conducted in August 2017 and September 2018. The samples were used for determination of total mercury (T-Hg) and organic mercury (org-Hg) concentrations, total organic carbon (TOC) content, and chemical composition. The atmospheric mercury concentration on the east shore side, 6.1–25.8 ng m −3 , was significantly higher than the value of 1.4–9.9 ng m −3 observed on the west shore side. The average concentrations of T-Hg in the forest soils of the west shore side and those of the east shore side were 0.081 ± 0.028 mg kg −1 and 0.496 ± 0.439 mg kg –1 , respectively. In the vertical distribution of T-Hg in the soil of the east shore side, a higher concentration was observed near the surface. For the vertical variations in T-Hg in the marine sediment, higher values were observed near the estuary, and the vertical variations in core samples showed an increase in mercury concentration toward the surface. The highest concentration of T-Hg in sediment, 9.5 mg kg −1 , which was 2 orders of magnitude higher than the background levels of this area, was found near the river mouth. The T-Hg, org-Hg, and TOC levels showed a positive correlation, suggesting that the rivers are the main sources of T-Hg and org-Hg in the bay. Although the fish sample containing a mercury content higher than the regulatory level for fish and shellfish of 0.4 mg kg −1 in Japan was only one of 42 samples, the percentage of org-Hg in fish samples was 91 ± 18%. Mercury released into the surroundings by the ASGM activities can be converted into methylmercury and affect the bay’s ecosystem.

PurposeDespite occupying only 0.5% of the global coastal ocean, mangroves play a disproportionately large role in the capture and retention of atmospheric carbon dioxide as organic carbon (OC) in its sediments. However, the capacity of mangrove sediments to store high amounts of OC has never been explained mechanistically. This study elucidates the role of reactive iron (FeR) in long-term carbon sequestration in mangrove sediments.Materials and methodsSediment samples of up to 1 m in depth were collected from six selected mangrove areas across the Philippines. The samples were characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF). A citrate-bicarbonate-dithionite reduction procedure was employed to extract FeR from the sediments. The OC concentration and δ13C signatures before and after FeR extraction were determined using a dichromate oxidation technique and isotope ratio mass spectrometry (IRMS), respectively.Results and discussionXRD diffractograms showed that the mangrove sediment samples varied in terms of mineralogical characteristics, which reflected their different parent materials. It was found that the OC concentration increased exponentially (OC = 8.38e0.37FeR; R2 = 0.88; p < 0.0001) with increasing FeR concentration. δ13C signatures of FeR-associated OC revealed that FeR preferentially preserved terrestrial over marine-derived organic matter. Finally, FeR was estimated to coprecipitate with up to 5.44 × 1012 g OC in mangrove sediments per year.ConclusionsThe findings of this study suggest that FeR is responsible for the preservation of OC, thus making mangrove sediments a “giant rusty sponge” for carbon. This mechanistic understanding of the long-term carbon storage in mangrove sediments could help draft better strategies for blue carbon initiatives that include the mangrove ecosystems.

Limited data have been published on the chemistry of urban soils and vegetation in the Philippines. The aim of this study is to quantify the concentrations of heavy metals (i.e., Cr, Ni, Cu, Zn, and Pb) in soils and vegetation in the urban landscape of Quezon City, Philippines, and to elucidate the relationships between soil properties and the concentration of heavy metals pertaining to different land uses [i.e., protected forest (LM), park and wildlife area (PA), landfill (PL), urban poor residential and industrial areas (RA), and commercial areas (CA)]. Soil (0–15 cm) and senescent plant leaves were collected and were analyzed for soil properties and heavy metal concentrations. Results revealed that the concentrations of heavy metals (i.e., Cr, Ni, Cu, Zn, and Pb) in urban soils were higher in areas where anthropogenic activities or disturbance (PL, RA, and CA) were dominant as compared to the less disturbed areas (LM and PA). Organic matter and available phosphorous were strongly correlated with heavy metal concentrations, suggesting that heavy metal concentrations were primarily controlled by these soil properties. The average foliar heavy metal concentrations varied, ranging from 0 to 0.4 mg/kg for Cd, 0–10 mg/kg for Cr, 2–22 mg/kg for Cu, 0–5 mg/kg for Pb, and 11–250 mg/kg for Zn. The concentrations of Cd and Cr exceeded the critical threshold concentrations in some plants. Leaves of plants growing in PL (i.e., landfill) showed the highest levels of heavy metal contamination. Our results revealed that anthropogenic activities and disturbance caused by the rapid urbanization of the city are major contributors to the heavy metal accumulation and persistence in the soils in these areas.

Ecosystem fires are stochastic and anthropogenic phenomena that affect critical soil processes. Nevertheless, environmental managers, policy-makers, and even scientists have often overlooked the induced transformations that fire does to soil organic matter (SOM), which sustains an ecosystem’s overall health. Here, we investigated the effects of simulated fire conditions on bulk SOM, water-extractable organic matter (WEOM), and vulnerability to microbial degradation. Sequential thermal decomposition experiments were carried out to investigate the effect of increasing temperature on C, N, δ¹³C, and δ¹⁵N of bulk SOM and WEOM. A microbial decomposition experiment was also done to determine the effects of burning on SOM degradability. Intermediate-intensity burns caused significant decreases in C and N concentrations in soils, as well as alterations in bulk SOM and WEOM properties. Conversely, the effects of low-intensity burns were less apparent in terms of bulk SOM content and stable C and N isotope composition. However, the results of the microbial decomposition experiment revealed that low-intensity burning resulted in elevated CO₂ emission that were significantly correlated with C concentration, δ¹³C values, and the C/N ratio of WEOM. These results provide evidence that low-intensity burning can have important consequences for soils, altering its organic components and releasing significant amounts of greenhouse gases. Thus, particular focus must be given to managing ecosystem fires and evaluating their impacts, especially because fire is still widely used in agriculture and forest management with frequency projected to increase in the coming years.

The limited carrying capacities of shallow tropical lakes render them more vulnerable to ecological problems like eutrophication. Unregulated human activities such as unsustainable aquaculture and urbanization can alter ecosystem dynamics rapidly, and this warrants more comprehensive researches than what has been previously conducted. Here, we presented an integrated assessment of the nutrient dynamics, phytoplankton diversity, and sediment geochemistry in Lake Palakpakin, a shallow tropical lake of volcanic origin, to understand its deteriorating ecological state. Water, phytoplankton, and sediment samples were collected, and in situ water quality measurements were done during wet and dry seasons in four critical areas in the lake, namely, the inlet, center, sanctuary, and outlet. Results revealed that high light extinction coefficient (1.13 m −1 ), high turbidity (28 NTU), high phosphate concentration (> 2.0.5 mg/L), and the abundance of Microcystis aeruginosa , Anabaena helicoidea , and Lyngbya sp. indicate that from a relatively healthy lake in 2008, Lake Palakpakin has become a eutrophic to hypereutrophic freshwater body. High concentrations of available nutrients such as N and P were detected in the center and sanctuary sediments, which drive the internal nutrient loading in the lake. We recommend that management efforts be directed towards a whole-ecosystem approach in addressing the problem of eutrophication, especially in shallow tropical lakes.

This study was conducted to evaluate the physical, chemical, and mineralogical characteristics of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Four sites along a catena were selected at an elevation of 75-112 m above sea level with an average annual rainfall of 3,000 mm and an average temperature of 28°C. Results indicate that the soils are deep, clayey, and reddish in color, which is indicative of the advanced stage of soil development. They also posses excellent physical condition (friable and highly porous) although they are plastic and sticky when wet as is usual for clayey soils. In terms of chemical characteristics, the soils are acidic with low CEC values and generally low in organic matter and nutrient contents. The clay mineralogy of the soils is dominated by halloysite and kaolinite with minor amounts of goethite and hematite, and they also have generally high dithionite-extractable Fe contents confirming the advanced stage of their development. The soils in the more stable slope positions (PL-1, PL-2, and PL-4) have generally similar characteristics and appeared more developed than the one in the less stable position (PL-3). The most important pedogenic processes that formed the soils appear to be weathering, loss of bases and acidification, desilification, ferrugination, clay formation and translocation, and structure formation. The nature of the parent rock and climatic conditions prevailing in the area as well as slope position appear to have dominant effects on the development of the soils..[PUBLICATION ABSTRACT]

In this study, concentrations of nickel (Ni) were quantified in the soils and plants in the agricultural areas of Salcedo watershed in Eastern Samar Island, Philippines. The quantity of total Ni in soils (TS-Ni) was significantly high with a mean of 1,409 mg kg⁻¹, while the soil available Ni (SA-Ni) was low with a mean of 8.66 mg kg⁻¹. As the levels of TS-Ni in the Salcedo watershed greatly exceeded the maximum allowable concentrations for agricultural soils, the site is not suitable for agricultural purposes. Despite significant TS-Ni levels, SA-Ni levels were very low due to tight binding between Ni and soil components. Consequently, all plants investigated did not meet the criterion for a Ni hyperaccumulator plant with low Ni contents (mean TP-Ni of 14.7 mg kg⁻¹). Comparison of Ni levels between food plants and its recommended daily intake (RDI) suggests that consumption of food-plants grown in the study area is unlikely to pose health risks. However, caution must be taken against combined consumption of food plants with high Ni levels or their prolonged consumption, as it can induce accumulation of Ni above RDI.