International audience | Burkholderia pseudomallei is the bacterium that causes melioidosis in humans. While B. pseudomallei is known to be endemic in South East Asia (SEA), the occurrence of the disease in other parts of the tropics points towards a potentially large global distribution. We investigated the environmental factors that influence the presence (and absence) of B. pseudomallei in a tropical watershed in SEA. Our main objective was to determine whether there is a link between the presence of the organism in the hydrographic network and the upstream soil and land-use type. The presence of B. pseudomallei was determined using a specific quantitative real-time PCR assay following enrichment culture. Land use, soil, geomorphology, and environmental data were then analyzed using partial least squares discriminant analysis (PLSDA) to compare the B. pseudomallei positive and negative sites. Soil type in the surrounding catchment and turbidity had a strong positive influence on the presence (acrisols and luvisols) or absence (ferralsols) of B. pseudomallei. Given the strong apparent links between soil characteristics, water turbidity, and the presence/absence of B. pseudomallei, actions to raise public awareness about factors increasing the risk of exposure should be undertaken in order to reduce the incidence of melioidosis in regions of endemicity.

International audience | Burkholderia pseudomallei is the bacterium that causes melioidosis in humans. While B. pseudomallei is known to be endemic in South East Asia (SEA), the occurrence of the disease in other parts of the tropics points towards a potentially large global distribution. We investigated the environmental factors that influence the presence (and absence) of B. pseudomallei in a tropical watershed in SEA. Our main objective was to determine whether there is a link between the presence of the organism in the hydrographic network and the upstream soil and land-use type. The presence of B. pseudomallei was determined using a specific quantitative real-time PCR assay following enrichment culture. Land use, soil, geomorphology, and environmental data were then analyzed using partial least squares discriminant analysis (PLSDA) to compare the B. pseudomallei positive and negative sites. Soil type in the surrounding catchment and turbidity had a strong positive influence on the presence (acrisols and luvisols) or absence (ferralsols) of B. pseudomallei. Given the strong apparent links between soil characteristics, water turbidity, and the presence/absence of B. pseudomallei, actions to raise public awareness about factors increasing the risk of exposure should be undertaken in order to reduce the incidence of melioidosis in regions of endemicity.

Lime or dolomite is commonly implemented to ameliorate soil acidity. However, the impact of dolomite on CO₂ emissions from acidic soils is largely unknown. A 53-day laboratory study was carried out to investigate CO₂ emissions by applying dolomite to an acidic Acrisol (rice-rapeseed rotation [RR soil]) and a Ferralsol (rice-fallow/flooded rotation [RF soil]). Dolomite was dosed at 0, 0.5, and 1.5 g 100 g⁻¹ soil, herein referred to as CK, L, and H, respectively. The soil pH₍H₂O₎ increased from 5.25 to 7.03 and 7.62 in L and H treatments of the RR soil and from 5.52 to 7.27 and 7.77 in L and H treatments of the RF soil, respectively. Dolomite application significantly (p ≤ 0.001) increased CO₂ emissions in both RR and RF soils, with higher emissions in H as compared to L dose of dolomite. The cumulative CO₂ emissions with H dose of dolomite were greater 136% in the RR soil and 149% in the RF soil as compared to CK, respectively. Dissolved organic carbon (DOC) and microbial biomass carbon (MBC) increased and reached at 193 and 431 mg kg⁻¹ in the RR soil and 244 and 481 mg kg⁻¹ in the RF soil by H treatments. The NH₄ ⁻-N and NO₃ ⁻-N were also increased by dolomite application. The increase in C and N contents stimulated microbial activities and therefore higher respiration in dolomite-treated soil as compared to untreated. The results suggest that CO₂ release in dolomite-treated soils was due to the priming of soil C content rather than chemical reactions.

The toxicity of dredged sediments from Guanabara Bay (Rio de Janeiro, Brazil) was evaluated using acute bioassays with Eisenia andrei and metal determination. The sediments were collected in August 2014 (winter) and February 2015 (summer) and in five areas distributed along the Bay: Port of Rio de Janeiro, Port of Niterói, Meriti River mouth, Iguaçu River mouth, and the Environmental Protection Area (APA) of Guapimirim. The sediments were mixed with a ferralsol (a representative Brazilian tropical soil) in proportions varying between 0 (pure soil) and 30%. The acute bioassays with E. andrei followed a standard protocol (ISO 11268-2:2012). Total metal determination in the sediments was performed by ICP-OES. The medium lethal earthworm concentration (LC₅₀) was estimated through PriProbit analysis. The sediments from the APA of Guapimirim, which is a control area at the Guanabara Bay, were the only ones whose total metal concentrations were in agreement with the limits established by Brazilian law for land disposal of dredged sediments. However, the sediments collected in the APA of Guapimirim were the most toxic ones among the study areas due to very high contents of salts in these materials. Winter sediments were generally more toxic compared to the summer ones due to the increase of metal concentrations and salt precipitation to bottom sediments during the winter. The exceptions were (i) the sediments from APA of Guapimirim, where the toxicity in the summer (LC₅₀ = 3.99%) and winter (LC₅₀ = 4.60%) were relatively similar to each other, since the toxicity is linked to salt in excess; and (ii) the Iguaçu River mouth, where the presence of mangrove areas might be associated with the filtering of pollution sources (winter LC₅₀ = 12.67%; summer LC₅₀ = 11.58%). In the Port of Rio de Janeiro, LC₅₀ obtained in the winter (7.30%) was almost three times lower than that found in the summer (19.64%). The sediments from Meriti River mouth showed the highest total metal concentrations, were the most toxic sediments among the study areas (excluding the APA of Guapimirim), and its winter LC₅₀ (6.64%) was almost twice lower than that obtained in the summer (12.55%). By following the same tendency, summer LC₅₀ (17.52%) found for the sediment collected in the Port of Niterói was also higher than the value found in the winter (12.34%). Finally, the dredged sediments from Guanabara Bay were toxic to earthworms in mixtures with pure ferralsol and winter samples were generally more toxic than the summer ones, in agreement with the increase of metal and salt concentrations during the winter.

Chlordecone (CLD), a highly persistent organochlorine pesticide commonly encountered in French West Indies (FWI) agricultural soils, represents a major source of contamination of FWI ecosystems. The potential of chemical reduction for remediation of CLD-contaminated soil has been investigated in laboratory pilot-scale 80 kg mesocosms for andosol, ferralsol, and nitisol from FWI banana plantations. Six cycles consisting of a 3-week reducing phase followed by a 1-week oxidizing phase were applied, with 2 % (dw/dw) Daramend® (organic plant matter fortified with zero valent iron) added at the start of each cycle. Complementary amendments of zero valent iron and zinc (total of 3 % dw/dw) were added at the start of the first three cycles. After the 6-month treatment, the CLD soil concentration was lowered by 74 % in nitisol, 71 % in ferralsol, and 22 % in andosol. Eleven CLD-dechlorinated transformation products, from mono- to penta-dechlorinated, were identified. None of them accumulated over the duration of the experiment. Six of the seven ecotoxicological tests applied showed no difference between the control and treated soils. The treatment applied in this study may offer a means to remediate CLD-contaminated soils, especially nitisol and ferralsol.

Soil cadmium (Cd) availability and uptake by cherry-red radish (Raphanus sativus) grown in Cd-contaminated soils after addition with wheat straw or composted pig manure were studied. The results indicated that wheat straw application promoted radish growth until the second harvest, while pig manure application improved radish biomass in Acid Ferralsols regardless of harvesting seasons. Application with pig manure might be more effective in lowering the Cd uptake by radish than wheat straw. Especially when pig manure of 11.9 g TOC kg⁻¹ amended into Acid Ferralsols, Cd contents in leaves and roots of radish decreased by 89.2 and 95.7 % at the second harvest, respectively. The changes in Cd fractions distribution in soils after application were contributed to the decline of Cd availability. Furthermore, significantly negative linear correlation (P < 0.05) between the ratio of humic acid (HA) and fulvic acid (FA) in soils and exchangeable Cd was also observed. However, the significantly negative relationship (P < 0.01) between soil pH and exchangeable Cd was merely found in pig manure-treated Acid Ferralsols. The increases in HA/FA ratio or pH values in soils after adding organic materials were also responsible for the decrease of Cd availability in soils and uptake by radish. Thus, it is recommended to stabilize soil Cd and reducing plant uptake by application with composted manure without or slightly contaminated with metals.

Burkholderia pseudomallei is the bacterium that causes melioidosis in humans. While B. pseudomallei is known to be endemic in South East Asia (SEA), the occurrence of the disease in other parts of the tropics points towards a potentially large global distribution. We investigated the environmental factors that influence the presence (and absence) of B. pseudomallei in a tropical watershed in SEA. Our main objective was to determine whether there is a link between the presence of the organism in the hydrographic network and the upstream soil and land-use type. The presence of B. pseudomallei was determined using a specific quantitative real-time PCR assay following enrichment culture. Land use, soil, geomorphology, and environmental data were then analyzed using partial least squares discriminant analysis (PLSDA) to compare the B. pseudomallei positive and negative sites. Soil type in the surrounding catchment and turbidity had a strong positive influence on the presence (acrisols and luvisols) or absence (ferralsols) of B. pseudomallei. Given the strong apparent links between soil characteristics, water turbidity, and the presence/absence of B. pseudomallei, actions to raise public awareness about factors increasing the risk of exposure should be undertaken in order to reduce the incidence of melioidosis in regions of endemicity.