When parts are more important than the sum

Folks, I welcome you to my LinkedIn portal for 2019. The long period of inactivity stemmed from being away on leave for 6 weeks, although, in this period, I was still guilt-ridden about the lack of constructive engagement on my profile. Here is my first stab at redemption, with the very first article for 2019.

I have previously discussed a paper we wrote on the heavy metal content of the former Lami municipal waste receptacle. For those from Fiji and the Pacific familiar with Suva and indeed Fiji, it is the same facility colloquially referred to as the “Lami Dump”. The article in question can be found here..

This article can be viewed in sequence from the aforementioned, as they both will deal with peer-reviewed scientific papers stemming from the research project. In this article, titled Study of heavy metal fractionation in the Lami municipal disposal facility, Fiji (click on link to take you to the open-access paper), we examined the partitioning of heavy metals in sediments and soils from the waste receptacle. Yes, there is a difference between them.

In soil, heavy metals are spread in different fractions. These fractions represent the sections of the soil in many ways. Notable fractions include: water-soluble (which means any metals in this fraction is very lightly retained and upon contact with water and in the right conditions, will be lost from the fraction), carbonate-held (held as carbonates of the metal, and somewhat more tightly-held than in water-soluble), ferromanganese-bound (held by minerals made of iron and manganese, yet more tightly-held than carbonate).

These fractions aren’t prescribed with any binding (sorry, couldn’t resist the pun) agreement. Thus, in your readings on the subject, you may find some researchers have different named fractions. What is agreed on though is, the more tightly the metal is retained in the fraction, the more aggressive the method to retrieve it from that fraction into solution. Solution here can be that in the lab, or in real-life, the soil solution which is the liquid portion of soil.

In our paper, we used the Tessier method, which is a prescribed set of extraction protocols to extract heavy metals from the following fractions:

• Water-soluble,
• Exchangeable
• Carbonate-held
• Ferromanganese-held
• Residual

Our work in this paper examined the most loosely-held levels of the metals, which we termed as bioavailable. The term captures the high probability of these metals being easily lost (due to being the most loosely held), and as a result, being available to flora and fauna (‘bio’ and ‘available’ conjoined). This information is more useful from an environmental toxicity standpoint as it helps establish the immediate risk rather than the whole amount of a metal, much of which may be so tightly-held that it would never be released.

This was the first such study and we focused on copper (Cu), zinc (Zn), lead (Pb) and nickel (Ni). To do our work, we collected soil samples from three parts of the facility reflecting various states of use (an immediately-discarded site – Site A, an active site – Site B and old site with no dumping for over a year – Site C). Our findings revealed high levels of Pb in Site A (109.0 mg/kg). Zn was the predominant metal across Sites B and C with 550.7 mg/kg and 206.8 mg/kg, respectively. Ni was present in the least amount with the highest value 8.7 mg/kg. In addition, Cu, Pb and Zn concentrations exceeded commonly used eco-toxicity threshold values. These are represented in succinct form in Figure 1.

Figure 1 Pie chart showing proportional representation of bioavailable heavy metals by site.

Worryingly, there were indications that considerable leaching of the studied heavy metals may have been occurring for long periods of time at the sites. It led to an important realization that even in areas with little industrialization, lack of adequate waste management controls could result in unusually high levels of heavy metals contamination of the soil.

Today, the former waste facility has been piled on and compacted with several meters of calcareous soil and the site remains off-limits to the public. There have been attempts to revegetate the site using Vetiver grass to hold the soil and allow for future rezoning into other uses. 

For aspiring students in the Pacific, it would be worth a proposal to investigate if there is any incidence of the metals listed above in the vicinity of the former facility and indeed, the nearby ocean. An article on December 30, 2018 (less than a month at the time of writing this article) revealed indiscriminate and wilful waste dumping on the foreshore that covers the facility. While closed for waste disposal, the area may quite likely still be a ticking environmental timebomb that needs a long and systematic monitoring regime.

The results raise concerns about the wellbeing of the communities living adjacent to the Lami municipal disposal facility that depend on the adjacent marine environment for their subsistence.

As usual, comments and feedback are welcome.

Shaneel :)

Reference

Chandra, S., Gangaiya, P., Togamana, C. and Prasad, S. Study of heavy metal fractionation in the Lami municipal disposal facility, Fiji, The South Pacific Journal of Natural and Applied Sciences, 2016, 34 (1) pp. 21- 28.