Evaluation of the impact of asbestos wastes on soils in Emene-Enugu, Southeastern Nigeria

Our plain-English summary of Evaluation of the impact of asbestos wastes on soils in Emene-Enugu, Southeastern Nigeria, by O. Igwe, O.V. Omonona, O.S. Onwuka, et al (Environmental Monitoring and Assessment, 2014).

The study

• Authors: O. Igwe, O.V. Omonona, O.S. Onwuka, O.D. Nnebedum
• Journal: Environmental Monitoring and Assessment
• Published: 2014;186(12):8063-80
• Read it: PubMed · Publisher

Abstract

This study investigated the impacts of asbestos wastes on soils in Emene-Enugu, southeastern Nigeria, generated by the activities of a major asbestos products manufacturing company in southeastern Nigeria. The methods of investigation included vertical electrical sounding (VES), 2-D horizontal resistivity profiling (HRP), induced polarization (IP) survey, chemical analysis of plant tissues and standard penetration tests of soil samples. The 2-D HRP and IP identified six closed waste pits alongside the two active pits. The VES revealed four geoelectrical layers in the area: from bottom to top; the inferred lithologies included dark shale, clay, gravel and recent sands. The geochemical data results revealed that Cd concentration of the soils of the waste pits is above the contaminated land exposure assessment soil guideline value for residential and allotment land uses. The geochemical pollution indices classified the soils as "unpolluted" to "extremely polluted". Bioconcentration factor of Pb in plant tissues was found to be above recommended limits of 0.045. The geotechnical parameters indices revealed that the soils varied from "very soft" to "stiff" and "very loose" to "medium". Soils of the active pits have very low strength and bearing capacity while closed pits have high strength and bearing capacity. It may be safe, therefore, to conclude that as the wastes are completely turned into soils, they will assume geotechnical properties similar to those of natural soils.

In plain English

This field study examined an asbestos-products factory's waste site in Emene-Enugu, southeastern Nigeria. The factory opened in 1963 and replaced asbestos with polyvinyl alcohol in 2000. The asbestos type is not named, and asbestos fibers in soil were not measured. They measured heavy metals in soil and a weed, soil chemistry, and soil strength. Electrical surveys located six closed pits besides two active ones. They analysed eleven soil samples (eight from pits, three controls) and drilled six boreholes. Pit soils generally had more lead, cadmium and chromium than controls, with exceptions such as low lead in the active-pit surface sample; pit cadmium exceeded a residential and allotment soil guideline value. Pollution indices rated the soils from "unpolluted" to "extremely polluted". The lead bioconcentration factor (plant level divided by soil level) exceeded the recommended 0.045. Control plants had the highest lead bioconcentration factors, which the authors said other human sources and natural geological processes may explain. Active-pit soils were very loose and soft to very soft; closed-pit soils were firm and stiff. The authors concluded that fully decomposed wastes will gain natural soils' bearing capacity.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Environmental field survey of a waste dumpsite using geophysical surveys, geochemical analysis of soil and plant tissue, and geotechnical (standard penetration) tests
• Who was studied: Soils and plants at the asbestos factory's waste disposal site in Emene, Enugu, southeastern Nigeria (eight waste pits). The samples were eleven soil samples (six from two closed pits, two from active pits, three controls from outside the dumpsite), plant tissues of Billygoat-weed (Ageratum conyzoides), and six boreholes. Dates of sampling are not given.
• Exposure: Wastes from an asbestos-product factory making roofing, ceiling and garden products. Its raw materials included cement and asbestos, with asbestos replaced by polyvinyl alcohol (PVA) since 2000. Wastes included asbestos–cement waste and fibre–cement waste, over 1,000 tons a year. The asbestos fiber type is not stated, and asbestos content in the soil was not measured.
• Main results:
  • Eight waste pits were identified at the site: six filled and closed (located by resistivity and induced polarization surveys) and two active.
  • Soils from the waste pits had pH 7.0 to 8.1 (slightly alkaline). Control soils had pH 5.0 to 5.3 (acidic).
  • The authors reported that lead, cadmium, chromium and total hydrocarbon were higher in waste-pit soils than in control soils. Table 2 shows exceptions. Lead in the active-pit surface sample is listed as below 0.001, against 24.39 in the surface control. Chromium in several closed-pit samples is listed as below 0.001, against 0.11 to 0.15 in the controls.
  • Cadmium in the waste pits was above the Environment Agency contaminated land exposure assessment (CLEA) soil guideline value for residential and allotment land uses.
  • Across all soil samples, including the controls, the geoaccumulation index for lead ranged from −0.62356 to 3.106582. For cadmium it ranged from 1.47106 to 7.14554.
  • Lead was classified from "unpolluted" to "moderately polluted" and cadmium from "moderately polluted" to "extremely polluted". The other metals were classified as "unpolluted".
  • The enrichment factor ranged from 0.00012 to 166.696 in closed-pit soils and from 0.0000404 to 112.516 in the active pit.
  • Of the metals assessed, only lead had a bioconcentration factor (the plant-tissue concentration divided by the soil concentration) above the recommended value. In Table 8 the recommended value for lead is 0.045.
  • The highest lead bioconcentration factors were in control plants from outside the site (5.32 leaf, 5.00 stem). The authors said these may be attributed to human-related sources other than asbestos waste disposal and to natural geological processes. In Table 3, the highest measured lead levels in plant tissue were in active-pit plants.
  • Soils from the active pits were very loose and soft. In Table 11, one active-pit borehole (borehole 6) was classified as very soft. Soils from the closed pits were described as firm and stiff.
• The authors' conclusion: The authors concluded that asbestos wastes negatively affected soil bearing capacity. They also concluded that as the wastes fully turn into soil, the soils will gain high bearing capacity like natural undisturbed soils.

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