Pollution of the Niger Delta with total petroleum hydrocarbons, heavy metals and nutrients in relation to seasonal dynamics

The African Niger Delta is among the world's most important wetlands in which the ecological effects of intensive oil exploitation and global change are not well documented. We characterized the seasonal dynamics and pollution with total-petroleum-hydrocarbons (TPHs), heavy-metals (HMs) and nutrient-loads in relation to climate-driven variables. High TPH concentrations up to 889 mg/L and HMs up to 13.119 mg/L were found in water samples, with pronounced spatio-temporal variation throughout the year. HM pollution index and contamination factor indicate serious ecological and human health hazards, especially for Cd, Cu, Hg, and Ni. Significant differences in TPHs/HMs were observed between sites and seasons, with correlations between TPHs-HMs, and climate-variables and TPHs-HMs. Nutrient levels, turbidity, salinity, temperature, and SO42- were high and interlinked with the variability of TPHs/HMs being greatest during wet season. These findings suggest an urgent need for improved pollution control in the Niger Delta taking into account the observed spatio-temporal variation and the exacerbation of effects in light of climate change. Given the high levels of contamination, further assessments of exposure effects and bioaccumulation in biota should include future climate change scenarios and effects on humans who intensively depend on the system for drinking water, food supply and livelihood.

Risk assessment of PAHs and N-PAH analogues in sediment cores from the Niger Delta

Chemical-surveys of sediments are source of information about historical-pollution in aquatic-ecosystems, because ecological/human-health risks may arise from polycyclic-aromatic-hydrocarbons (PAHs) and nitrogen-PAHs presence in aquatic-environments, particularly sediments, where they partition. Despite this, sediment-PAHs/N-PAHs have not been reported in the Niger Delta. This study investigated vertical-profiles of PAHs/N-PAHs in 2 cm-intervals-segments from Bonny Estuary, Niger Delta. Analysis showed that ƩPAHs/ƩN-PAHs in segments ranged from 8699 to 22,528 μg/kg and 503 to 2020 μg/kg, respectively. Abundant-PAH/N-PAH are 2,6-dimethyl-naphthalene and benzo[a]acridine. PAHs/N-PAHs in the samples appeared to be from petrogenic and pyrogenic-sources. Petrogenic-PAHs/N-PAHs were predominated by 2-, 3-rings, alkylated-substituents, while, pyrogenic-PAHs/N-PAHs were dominated by 4-, 5-, 6-rings. Surface-sediments were dominated by petrogenic-PAHs/N-PAHs while, deeper-cores were heavily-contaminated with pyrogenic-PAHs/N-PAHs. ƩPAHs exceeded the ISQGs and PELs of CSQGs. Ʃ-quinoline/Ʃ-acridine exceeded the guidelines for protection of aquatic-life. Furthermore, there are concerns over toxic-ratios >70% in the estuary. Such surveys may be helpful in future sediment-management-decisions for contaminated-systems and long-term-monitoring of sediments to assess remediation/recovery. CAPSULE: Distinct sources of PAHs and N-PAHs exist in the Niger Delta ecosystem and, there are concerns over toxic ratios >70% in the oil rich region and the potential for adverse biological effects.

Quantitative assessment data of PAHs and N-PAHs in core sediments from the Niger Delta, Nigeria

Polycyclic aromatic compounds (PACs) pollution has been the focus of environmental research, mostly due to their mutagenicity, carcinogenicity, teratogenicity and genotoxicity. Concentrations of polycyclic aromatic hydrocarbons (PAHs) and the nitrogen-containing analogues (N-PAHs) (which tend to accumulate in sediments rather than water) was measured in 2 cm intervals segments from Bonny Estuary, Niger Delta using GC–MS. Data showed that PAHs/N-PAHs levels ranged from 8699 to 22,528 µg/kg and 503–2020 µg/kg, respectively. Furthermore, the data revealed that ƩPAHs level in the estuarine segments was > 45% higher than DPR/EGASPIN intervention limit. This gives insight on PAHs/N-PAHs contamination in the oil rich region.

In Vivo Genotoxicity of Rice Husk Biochar on Eudrilus eugeniae in Soil

Biochar (char-product), generated by pyrolyzing organic materials, is produced for the intended use of land application to promote carbon sequestration, soil improvement and crop-yield. Despite the benefits biochar applications offers, scientific probing on impacts that may result from amendments with biochar is still fragmented. In this study, impact of biochar on Eudrilus eugeniae DNA was investigated. Rice-husk biochar was applied to soil at rates up to 80% d/w and earthworms were exposed for 35-day. Impact on DNA was measured using electrophoresis-gel-extraction-method. Data obtained showed that biochar application over 25% resulted in decreased survival. Electrophoresis-gel-analysis showed that DNA decreased from 450 to 300 bp in biochar soils (p = 0.002). Biochar rates (5%-25%) induced DNA damage. The DNA showed smeared bands or tail; indicating DNA degradation and/or damage. DNA damage is a clear evidence of negative impact of biochar(s) to soil-biota; suggesting that loading of soil with biochar could have serious consequences on soil-fauna.

Modulation of PAH toxicity on the freshwater organism G. roeseli by microparticles

Polycyclic aromatic hydrocarbons are widespread and environmentally persistent chemicals that readily bind to particles in air, soil and sediment. Plastic particles, which are also an ubiquitous global contamination problem, may thus modulate their environmental fate and ecotoxicity. First, the acute aqueous toxicity of phenanthrene in adult Gammarus roeseli was determined with a LC₅₀ of 471 μg/L after 24 h and 441 μg/L after 48 h. Second, considering lethal and sublethal endpoints, effects of phenanthrene concentration on G. roeseli were assessed in relation to the presence of anthropogenic and natural particles. The exposure of gammarids in presence of either particle type with phenanthrene resulted after 24 and 48 h in reduced effect size. Particle exposure alone did not result in any effects. The observed reduction of phenanthrene toxicity by polyamide contradicts the discussion of microplastics acting as a vector or synergistically. Especially, no difference in modulation by plastic particles and naturally occurring sediment particles was measured. These findings can most likely be explained by the similar adsorption of phenanthrene to both particle types resulting in reduced bioavailability.

Influence of biochar aged in acidic soil on ecosystem engineers and two tropical agricultural plants

Biochar amendment to soil is predicted globally as a means to enhance soil health. Alongside the beneficial result on soil nutrient availability and retention, biochar is presumed to increase soil macro / microbiota composition and improve plant growth. However, evidence for such an effect remains elusive in many tropical agricultural soils. The influence of biochar aged in soil was assessed on soil microbiota, macrobiota (Eudrilus eugeniae), seedling emergence and early plant growth of Oryza sativa and Solanum lycopersicum in tropical agricultural soil, over a 90 d biochar-soil contact time. Results showed negative impacts of increased loading of biochar on the survival and growth of E. eugeniae. LC₅₀ and EC₅₀ values ranged from 34.8% to 86.8% and 0.9-23.7% dry biochar kg^-1 soil, over time. The growth of the exposed earthworms was strongly reduced (R² = -0.866, p < 0.05). Biochar significantly increased microbiota abundance relative to the control soil (p < 0.001). However, fungal population was reduced by biochar addition. Biochar application threshold of 10% and 5% was observed for (O. sativa) and (S. lycopersicum), respectively. Furthermore, the addition of biochar to soil resulted in increased aboveground (shoot) biomass (p < 0.01). However, the data revealed that biochar did not increase the belowground (root) biomass of the plant species during the 90 d biochar-soil contact time. The shoot-to-root-biomass increase indicates a direct toxic influence of biochar on plant roots. This reveals that nutrient availability is not the only mechanism involved in biota-biochar interactions. Detailed studies on specific biota-plant-responses to biochars between tropical, temperate and boreal environments are needed to resolve the large variations and mechanisms behind these effects.

Impact of nitrogen-polycyclic aromatic hydrocarbons on phenanthrene and benzo[a]pyrene mineralisation in soil

When aromatic hydrocarbons are present in contaminated soils, they often occur in mixtures. The impact of four different (3-ring) nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) on ^12/14C-phenanthrene and ^12/14C-benzo[a]pyrene (B[a]P) mineralisation in soil was investigated over a 90 d incubation period. The results revealed that both ^12/14C-phenanthrene and ^12/14C-benzo[a]pyrene showed no significant mineralisation in soils amended with 10mgkg ^-1 and 100mgkg ^-1 N-PAHs (p>0.05). However, increases in lag-phases and decreases in the rates and extents of mineralisation were observed, over time. Among the N-PAHs, benzo[h]quinoline impacted ¹⁴C-phenanthrene mineralisation with extended and diauxic lag phases. Furthermore,^12/14C-B[a]P and ¹⁴C-benzo[a]pyrene-nitrogen-containing polycyclic aromatic hydrocarbons (¹⁴C-B[a]P-N-PAHs) amended soils showed extensive lag phases (> 21 d); with some ¹⁴C-B[a]P-N-PAH mineralisation recording <1% in both concentrations (10mgkg ^-1 and 100mgkg ^-1), over time. This study suggests that the presence of N-PAHs in contaminated soil may impact the microbial degradation of polycyclic aromatic hydrocarbons (PAHs) and the impact was most likely the result of limited success in achieving absolute biodegradation of some PAHs in soil.

Assessment of the effects of phenanthrene and its nitrogen heterocyclic analogues on microbial activity in soil

Microbes are susceptible to contaminant effects, and high concentrations of chemical in soil can impact on microbial growth, density, viability and development. As a result of relative sensitivity of microbes to contaminants, toxicity data are important in determining critical loads or safe levels for contaminants in soil. Therefore the aim of this study was to assess the impact of phenanthrene and the 3-ring nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) on soil microbial respiration. Soil samples were amended with phenanthrene and its 3-ring nitrogen-containing analogues and respiration rates (using substrate induced respiration), CO₂ production inhibition and/or stress and total culturable microbial numbers were measured over a 90 days soil-contact time. The study showed that inhibition of phenanthrene amended soils occurred in the first 60 days, while the nitrogen-containing analogues impacted on respiration with increased concentration and contact time. Time dependent inhibitions were more than 25 % portraying N-PAHs toxic and inhibitory effects on microbial synthesis of the added carbon substrate. Further, statistical analysis of data revealed statistically significant differences in the respiration rates over time (p < 0.05). This suggests that soil microorganisms may be more sensitive to N-PAHs in soil than the homocyclic PAH analogues. This current study provides baseline toxicity data to the understanding of the environmental impact of N-PAHs, and assists science-based decision makers for improved management of N-PAH contaminated sites.

The incrimination of Aedes (stegomyia) aegypti as the vector of Dirofilaria repens in Nigeria

Six local species of culicides were identified as the common mosquitoes in Zaria, out of 15 species captured using various adult and larval collection methods. These common culicides are Culex pipiens fatigans, Anopheles gambiae grp., Mansonia africana, Culex pipiens pipiens, Aedes (stegomyia) aegypti and Aedes vittatus. They were each fed directly on a local dog naturally infected with Dirofilaria repens to evaluate their refractoriness/susceptibility to dirofilarial infection. In a number of donor-feeding trials, 39. 4% Culex pipiens fatigans; 58.9% An gambiae grp.; 60.5% Mansonia africana; 1.8% of Culex pipiens pipiens; 23.4% Ae aegypti and 3.3% of Ae vittatus successfully fed on the microfilaraemic host. Only Aedes aegypti was susceptible to the infection as all 40 (100%) Ae aegypti reaching 10-14 day post-blood meal had infective (L(3)) larvae of D. repens. The remaining five species were refractory. The microfilariae in the five non-susceptible mosquitoes were always found trapped in the blood meal in the insects midgut (stomach). These trapped microfilaria were dead by the 2nd day in the insect's midgut. However, in the susceptible Ae aegypti, the microfilariae were set free from the blood meal in the midgut and within 24h migrated to the malpighian tubules (MT) of the mosquitoes. All Ae aegypti dissected 5-7 day post-infective blood meal showed the typical quiescent sausage stage (L(2)) larvae in the malpighian tubules. At day-10 post-blood meal, relatively active infective (L(3)) larvae of D. repens were found in the MT; and by day 12-14, highly motile infective larvae had reached the insect's head and proboscis, with infective larvae occasionally oozing out during dissection through the tip of the proboscis. The rate of development of D. repens to infective larvae was faster in mosquitoes infected in July when the environmental temperature was 24.5 degrees C than those infected in November when the temperature was 22.5 degrees C. The latter were delayed for 4 days. The breeding sources of Ae aegypti, the local vector implicated were also identified. As no particular vector of this zoonotic filaria has been identified previously in Nigeria, these findings could make any control programme more focussed and easier.

Canine filariasis in Zaria, Nigeria

Microscopic examination of blood samples from dogs in Zaria, Nigeria indicated the prevalence of canine filariasis to be 12.7%. The survey demonstrated three species of canine filariae, namely D. repens (8.9%). D. immitis-like parasite (2.5%), and an unidentified species of filaria with a prevalence of 4.4%.