| || || Heavy metals -- Environmental aspects -- Solomon Islands -- Marovo Lagoon|
| || || Heavy metals (Cr, Pb, Cd, Cu) in sediment and bivalves and nutrients (phosphate and nitrate) in Marovo Lagoon, Western Province, Solomon Islands|
Author: Boboria, Dickson Michael
Institution: University of the South Pacific.
Subject: Heavy metals -- Environmental aspects -- Solomon Islands -- Marovo Lagoon, Sediments (Geology) -- Heavy metal content -- Solomon Islands -- Marovo Lagoon , Water -- Pollution -- Solomon Islands -- Marovo Lagoon
Call No.: Pac TD 196 .M4 B63 2014
Copyright:40-60% of this thesis may be copied without the authors written permission
Abstract: Poor waste management and degradation of natural forests are a great concern in the South Pacific countries as these could lead to the coastal deterioration of the marine and lagoon environments. An investigation of the water quality of the Marovo Lagoon was carried out in early January, 2014 at a total of fifteen sites including ten stations for both sediments and water samples and five different sites for the bivalve samples. The collected sediment, bivalves and water samples were used to determine heavy metal (Cr, Pb, Cd, and Cu) and nutrient (NO3, - PO4 3-) pollution in the area. The physical and chemical parameters for water (pH, DO, salinity, turbidity) were also tested on site and showed the following ranges: pH (5.12 –7.86), salinity (32.1 – 36.6 0/00), DO (4.37 –7.89 mg /L), temperature (21.2 – 25.30C) and turbidity (140 – 1500 NTU). The dissolved oxygen is at normal levels but an increased turbidity level may represent high sedimentation and microbial activities in the lagoon, while the salinity may indicate less evaporation and fresh water influences in the lagoon. The concentrations of the metals in the analyzed sediment reference material (PACS-1) agreed generally quite well with the certified values and reasonable metal recoveries were practically achieved for all the tested metals. The total metals in the sediment samples appeared in the following order: Cu > Pb > Cr > Cd with the respective ranges of Pb (74.8 – 371 μg/g), Cu (144 – 358 μg/g), Cr (75–351 μg/g) and Cd (24.7 – 47.1 μg/g). This general pattern was also evident for the total metals in the bivalve tissues with the order of: Cd < Cr < Cu < Pb and the relative observed ranges: Cd (1.70 – 10.2 μg/g), Pb (24.0 – 85.5 μg/g), Cr (9.34 – 41.8 μg/g) and Cu (47.0 – 76.0 μg/g). However, the nutrient analyses showed the respective ranges of 1.23 – 136 μg/mL and 0.211– 30.9 μg/mL for PO4 3- and NO3 - but were generally low for all sites except for South Sege and Ngai Passage. The relationship between the sediment metals, the soft tissues metals and the nutrient levels can be explained by the poor hydrodynamic system of the lagoon. The data for the metals in both sediments and bivalves showed values greatly exceedingly or comparable to the ERL and TEL of the Sediment Quality Guidelines of NOAA and the sediment data of Naidu et al. (1991) for the same sites. As for nutrients, they were above the standards the ANZECC, (2000) guidelines for inshore marine waters and Naidu et al. (1991). However, they ii were still lower than the Australia and New Zealand standard guidelines and comparable to other Pacific studies indicating a potential ecological impact in the studied area in the future. The calculated Igeo generally showed values of less than 1, reflecting non-polluted environments. The calculated values for dermal contact with sediments (DCCS) and bivalve (DCCB) and ingestion of sediment (IS) and bivalves (IB) also showed values less than 1 mg/kg for all the studied metals, indicating less potential health risk in the lagoon. In general the DCCS, DCCB, IS and IB values showed less Pb risk for both children and adults for the entire study with values comparable to the background level of Pb of 0.46 mg/kg/day. The Wilcoxon test showed a significant result for the sediment data reflecting the increased levels of metals in sediments in the Marovo Lagoon over the years in relation to the Naidu et al. (1991) data for the same sites. The major identified human sources of contaminants in the lagoon include mining, domestic waste, commercial products (paints, Pb batteries, sewage dumping and medical waste), volcano eruptions and waste from logging machinery, applications of fertilizers in the oil palm plantation, small scale agricultural activities and advanced weathering of soil, sewage waste and run off from forest floor and urban sites. In general, the complex reef system and the narrow passages of the lagoon restrict the exchange of contaminants with the open sea categorizing Marovo as a wind mixing lagoon.