Analyse the need for monitoring the environment

What this dot point is asking

NESA wants you to explain why chemical analysis of the environment matters, identify the contaminants worth monitoring (cations, anions, organic pollutants, dissolved gases), and recognise that the choice of analytical technique depends on what you are looking for and at what concentration.

The answer

Why monitor at all

The environment is a chemical system in which human activity adds species that the natural cycle cannot remove fast enough. Without monitoring, those species accumulate to harmful levels before symptoms appear in plants, animals or people. The three main reasons to monitor are:

• Public health. Heavy metals (lead, mercury, cadmium), nitrate, fluoride and organic micropollutants are toxic at concentrations far below the threshold of taste or smell.
• Ecosystem health. Eutrophication from phosphate and nitrate runoff, acid mine drainage, and chloride from road salt all damage aquatic ecosystems long before they affect drinking water.
• Regulatory compliance. The Australian Drinking Water Guidelines (ADWG), state EPA licences and the National Pollutant Inventory all set numerical limits. Industries must demonstrate compliance by measurement.

What we typically monitor

Typical concentration limits (ADWG)

To choose the right technique you have to know the order of magnitude expected. Selected ADWG values:

• Lead $Pb^{2+}$: 10 ppb (0.01 mg/L)
• Mercury $Hg^{2+}$: 1 ppb
• Copper $Cu^{2+}$: 2 mg/L (2000 ppb)
• Nitrate $NO_3^-$: 50 mg/L (infants)
• Fluoride $F^-$: 1.5 mg/L
• Sulfate $SO_4^{2-}$: 250 mg/L (taste)

Concentrations in the ppb range cannot be measured by classical wet chemistry. You need an instrumental technique with a low detection limit and high specificity.

Qualitative vs quantitative

Qualitative analysis identifies what is in the sample. Flame tests, precipitation reactions and complexation tests are qualitative; you observe a colour or a precipitate and conclude the species is present.

Quantitative analysis measures how much. Gravimetric analysis, titration, colourimetry, UV-vis spectrophotometry and AAS are all quantitative; you obtain a number with units. Quantitative methods are usually preceded by qualitative ones, because you have to know what you are measuring before you measure it.

Choosing a technique

The choice depends on three things:

1. What. Metal ions favour AAS or ICP. Anions favour precipitation titration, ion chromatography or colourimetry. Organic species favour mass spectrometry, IR or NMR.
2. How low. ppm-level targets allow wet chemistry. ppb-level targets force instrumental methods.
3. How specific. A sample with many similar species (sea water, soil extract) needs a separation step or a highly specific detector. AAS uses an element-specific lamp; mass spectrometry uses mass-to-charge ratios.

The rest of Module 8 is about each of these techniques in detail.

Examples in context

Example 1. WaterNSW continuous monitoring of the Wivenhoe spillway and Warragamba intake. WaterNSW operates a network of automatic monitoring stations on the rivers feeding Sydney's drinking-water reservoirs. Each station logs pH, dissolved oxygen, conductivity and turbidity every 15 minutes. Annual heavy-metal screens are run via AAS at the central Potts Hill lab, with detection limits below 1 $\mu$g L$^{-1}$ for lead, cadmium and arsenic. If a reading exceeds the 10 $\mu$g L$^{-1}$ Australian Drinking Water Guidelines limit, the station triggers an automatic alert and engineers escalate to a full ICP-MS scan. The HSC framework of qualitative tests followed by quantitative confirmation maps directly onto this real workflow.

Example 2. Air quality monitoring at NSW EPA Liverpool station. The Sydney south-west air-quality station monitors $NO_2$ by chemiluminescence and $SO_2$ by UV fluorescence, alongside $PM_{2.5}$ by beta-attenuation. During the 2019-2020 Black Summer bushfires, the station recorded $PM_{2.5}$ above 200 $\mu$g m$^{-3}$, more than 10 times the WHO daily limit of 15 $\mu$g m$^{-3}$. The data triggered school closures and asthma-medication free-supply distribution across south-west Sydney. The HSC justification of monitoring (protect health, demonstrate regulatory compliance, provide early warning of environmental incidents) is exactly what the EPA cited when defending the station's $4 million annual budget.

Try this

Q1. State three reasons why environmental monitoring of cations and anions is necessary, with one example pollutant for each. [3 marks]

• Cue. Health (lead in drinking water), ecosystem (nitrate in waterways), regulatory compliance (sulfate in industrial discharge).

Q2. A water sample is reported to contain 0.025 mg L$^{-1}$ of arsenic. Calculate the concentration in mol L$^{-1}$ and compare to the Australian Drinking Water Guidelines limit of $1.3 \times 10^{-7}$ mol L$^{-1}$. [3 marks]

• Cue. $[As] = 0.025 \times 10^{-3} / 74.92 = 3.34 \times 10^{-7}$ mol L$^{-1}$; this is 2.6 times the guideline; remediation required.

Q3. A council reviews monitoring strategy for a creek downstream of a copper mine. (a) Identify two suitable techniques and justify each. (b) State one pollutant that requires a part-per-billion detection limit. (c) Outline how a calibration curve enables quantitative reporting. [2+1+2 marks]

• Cue. (a) AAS for trace metals (ppb sensitivity), colourimetry for nutrients (rapid, low cost). (b) Cadmium or mercury. (c) Standards of known concentration measured to plot $A$ vs $c$; unknown $A$ converts via the line equation.