GASEOUS PROFILE AND AIR POLLUTION TOLERANCE INDICES OF SOME PLANTS AROUND THE GAS FLARING SITE IN UMUEBULU COMMUNITY, ETCHE LOCAL GOVERNMENT AREA, RIVERS STATE, NIGERIA

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ABSTRACT

The study examined the gaseous profile and air pollution tolerance index (APTI) of some plants around the gas flare site in Umuebulu Community in Etche Local Government Area of Rivers State, Nigeria. Four physiological and biochemical parameters: relative water content, ascorbic acid, total chlorophyll and pH of the leaf extracts were used to compute the APTI values. Plants were classified into three categories of sensitivity: APTI < 8.22 = sensitive, APTI 8.23 to 8.25 = intermediate and APTI > 8.26 = tolerant. The study quantified eight gases using eight Crowcon Gasman gas monitors. A Global Position System (GPS) was used to measure the longitude, latitude and elevation of the area before taking the readings from the flare site. The readings were taken for two weeks in each season, with February for dry season and October / November for rainy season, from four different locations designated as locations A, B, C and D. Micro-climatic features of the study area were determined by measuring the wind direction, wind speed, temperature and relative humidity, using mini-total station (Envi-monitor Model 08-1511). At each location readings were randomly monitored in the morning, afternoon and evening. Plants were collected randomly from the experimental and control sites and were used to determine their APTI values. Soil samples were randomly collected from the experimental site at four different locations and all readings were taken in triplicates. Eleven (11) plant species had significantly (P < 0.05) higher APTI than the other nine (09). The eleven were Elaeisguineensis (10.47 ± 0.02) / Manihot esculenta (10.05 ± 0.020),Chromolaenaodorata (9.84 ± 0.09),  Ocimumgratissimum (9.44 ± 0.01),  Anthocleistavogelii (9.38 ± 0.03), Panicum maximum (9.26 ± 0.012),Carica papaya (9.11 ± 0.05), Phyllanthus discoideus (8.81 ± 0.01) / Phyllanthus muellerianus (8.76 ± 0.03) , Ixora coccinea (8.31 ± 0.14) and  Solanum incanum (8.30 ± 0.00), and were the tolerant plants. The others Alchorneacordifolia, Sidaacuta, Psidium. guajava, Musa sapientum, Mangiferaindica, Millettiathonningii, Acalypha ciliate, Newbouldialaevisand Combretum platypterum had lower APTI values, and were the sensitive plants. Vernonia amygdalinawas the only moderately tolerant plant found. Eight out of the twenty-one plants studied were tolerant at both control and experimental sites, while seven were sensitive at both sites, six were not tolerant or sensitive at both sites. T-test between experimental and control plants showed that the APTI values of most of the control plants were significantly (P < 0.05) higher than those of the experimental plants. The physiological parameters showed higher ascorbic acid content, lower total chlorophyll content, lower relative water content and variable pH leaf extract of the experimental plant than those of the control. Gaseous profile showed that HCN and SO2 had no significant differences in all locations. Ammonia (NH3), CO, Cl2, and NO2 were significantly (P < 0.05) higher at location A (gas flare site) than in other locations.  For daily emissions HCN, Cl2 and NO2 showed no significant differences in all the periods of the day but H2S, CO and SO2 had high emissions in the evenings. For seasonal emissions there were significant (P < 0.05) differences between the emissions during rainy season and dry season for all gases, except H2S.The concentrations of H2S, HCN, NH3, SO2, NO2 and CH4 were higher than the Nigerian and United States National ambient air quality standard but CO and Cl2 are within the permissible limits.  Data for heavy metal concentration in the soil of Umuebulu indicated that the mean values of Ni, Fe, Cr, Zn, Al, Hg, Mn, Mo, As and Ag were relatively higher than the threshold critical levels, while Pb, Cd, Cu and Co had low optimal range and low critical values for toxicity (FEPA/USEPA). The pollution of the soil was thus remarkable, in which case animals and plants in the area are under threat of long term contamination.  The result from the analysis of the mineral nutrient showed that K, Ca, Mg, Na, P, H, CEC, N2, O.M, C, K2Cl, H2O, Coarse Sand, Fine Sand, Silt and Clay were all concentrated in the soil and the mineral nutrient contents were within the USEPA/FEPA guideline. The result of micro – climatic elements showed variations at different period of the day. Effect of the gas flaring activities increased the temperature of the area. Increase in temperature affects the humidity, wind speed and wind direction of the area, due to increase in the toxic gaseous emissions. It is recommended that gas flaring should be stopped completely and plants with high APTI values be grown near pollution prone areas. These plants would absorb and in turn screen off certain harmful gaseous pollutants, which contribute to green house effects, global warming and climate change, while sensitive plants should be planted as phyto-indicators of air pollution in urban and industrial areas.