Evaluation of Para Dichlorobenzene

Evaluation of para dichlorobenzene as used in “Deo Blocks” for urinals in the South African market

Prepared by: Donavin Hawker (N. Dip Chemical Engineering) 

March 2013

Product Usage & costing for South Africa


1,4 dichlorobenzene is commonly known as para dichlorobenzene or PDB. It is primarily used as a masking agent/deodoriser for urinals due to its nature as a volatile organic compound (VOC).  It is detectable by strong pungent odour at a low threshold value of 15 ppm. 

Health Concerns

The primary exposure to 1,4-dichlorobenzene is from breathing contaminated indoor air specifically in urinals. 

  1. Acute (short-term) exposure to 1,4-dichlorobenzene, via inhalation in humans, results in irritation of the skin, throat, and eyes. 
  2. A correlation between exposure to 1,4-dichlorobenzene and decrease in lung function has been shown (Elliot et al, 2006).
  3. Chronic (long-term) 1,4-dichlorobenzene inhalation exposure in humans results in effects on the liver, skin, and central nervous system (CNS) 
  4. 1,4-dichlorobenzene is a proven endocrine disruptor.
  5. Risk of lesions in the nasal (respiratory and olfactory) epithelium
  6. Mild liver and/or kidney lesions
  7. Extra cancer cases due to the mitogenic properties of 1,4-dichlorobenzene (a threshold effect). 

ECHA (European Chemicals Agency) committee has concluded that the risks from the uses of 1,4-dichlorobenzene in air fresheners and toilet blocks are not adequately controlled” for consumers. 


EPA has classified 1,4-dichlorobenzene as a Group C, possible human carcinogen.1 

ECHA (European Chemicals Agency) has implemented a restriction against use in urinal deoblocks for 1,4-dichlorobenzene due to health concerns.2

Food residue

Paradichlorobenzene was detected in a wide range of prepared foods during the U.S. Food and Drug Administration’s (FDA) Total Diet Study. 

  1. Of the 51 prepared foods analyzed for paradichlorobenzene, 29 foods had one or more samples with levels above the limit of quantification
  2. Researchers evaluated fresh vegetables purchased at retail outlets in the United Kingdom for the presence of various chlorobenzenes
  3. Paradichlorobenzene was detected in 61% of samples analyzed. Bean seeds (0.717 μg/kg fresh weight) and tomato peels (0.619 μg/kg fresh weight) had the highest levels detected.

Environmental Impact

Listed as Aquatic Acute 1: Hazardous to the aquatic environment, acute hazard category 1

Aquatic Chronic 1: Hazardous to the aquatic environment, chronic hazard category 1 

H400: Very toxic to aquatic life

H410: Very toxic to aquatic life with long lasting effects. 


Researchers fed 10 young Peking ducks 0.5% paradichlorobenzene in their diet for 35 days. By the end of day 28, three ducks had died and the survivors showed decreased growth rates. 

Fish and Aquatic Life
Researchers exposed rainbow trout (Oncorhyncus mykiss) and zebrafish (Danio rerio) to water treated with paradichlorobenzene. The 48-hour LC50 for rainbow trout was 1.18 mg/L, and the 48-hour LC50 for zebrafish was 4.25 mg/L. 

Looking at para dichlorobenzene on cost basis 

Table 1

Para Dichlorobenzene data3  
Mass loss due to sublimation 1.6 – 4.6 x 10-3g/min 1
Solubility in water at 200C 0.08 g/L
Pricing (average price from 4 suppliers) R42/kg
Mass of block 40 g
Calculation assumptions  
Flush volume – low volume flush urinal 2 litres
Low throughput – assume 4 persons/hour (10 hour day) 40 flushes/day – 1200 flushes/month
High throughput – assume 7 persons/hour (10 hour day) 70 flushes/day – 2100 flushes/month

No empirical data can be determined on replenishment frequency for para dichlorobenzene in urinals, hence this data is calculated from physical/chemical data tables. 

Loss of mass is due to sublimation as well as limited solubility in water. It can be assumed that there is also some loss due to mechanical erosion & incoherence of the crystalline block.

From ECHA “1,4-dichlorobenzene products

The 1,4-dichlorobenzene products are solid at room temperature and sublime gradually into surrounding air. Their longevity is mainly affected by i) size of the product and ii) the surrounding room temperature. If the block is wet – the sublimation rate may be reduced; instead, some substance may be dissolved into water. 

Based on information from RPA (2010), it is assumed, that an 1,4-dichlorobenzene air freshener or toilet block will last 21 days in a temperature of 200C and 10 days in a temperature of 250C. In the exposure assessment an average product (air freshener or toilet block) is assumed to weigh 80g. 

Calculated total mass loss of para dichlorobenzene would be as follows:- 

Table 2

Sublimation loss 2.3 – 6.6 g/day
Solubilisation – low throughput 8.4 g/day
Solubilisation – high throughput 16.8 g/day
Total mass loss/day – low throughput 10.7 g – 15 g
Total mass loss/day – high throughput 19.1 – 23.4 g

Using data above to calculate replenishment rates & costs of use:-

Table 3

No. of days before replenishment required – 2 – 4 days
Cost of use for para dichlorobenzene  – low throughput R18,90/urinal/month
Cost of use for para dichlorobenzene – high throughput R29,50/urinal/month

This correlates with data from ECHA as above. 

Laboratory trial of Green-Worx Cleaning Solutions supplied Pee Island

In field trials, we compare the traditional para dichlorobenzene deo-blocks vs. green “biological based” alternatives to determine replenishment frequency, as well as cost comparisons.



  • Para dichlorobenzene causes numerous health & environmental problems & is being banned/phased out of urinal cakes in a number of countries.
  • Dichlorobenzene deoblocks does not solve the cause of the malodour, neither do they disinfect/clean the urinal.
  • PDB deoblocks act solely as a masking agent.
  • The PDB deoblocks need frequent replacement.
  • Biological based products are available as environmentally friendly replacements which work at the root of the problem of malodour breaking these compounds down.
  • Odorite range products utilise surface cleaning action of surfactants + subtilis bacteria to provide a visually pleasing urinal, as well as being fragranced.
  • Odorite range of products need less frequent replacement & are more cost effective (days to replenishment, as well as no. of flushes) to use than PDB deoblocks.
  • Laboratory tests have proven that Odorite products act to remove 99.9% of bacteria from urinals. 
  1. United States Environmental Protection Agency – Evaluation Document http://www.epa.gov/ttnatw01/hlthef/dich-ben.html
  2. European Chemicals Agency (ECHA) Annex XV Restriction Report – 1,4 dichlorobenzene http://echa.europa.eu/documents/10162/3f467af2-66e0-468d-8366-f650f63e27d7
  3. National Pesticide Information Centre http://npic.orst.edu/factsheets/PDBtech.pdf
  4. Department of Trade & Industry – Trade Statistics – SA Import Value HS8 http://tradestats.thedti.gov.za/TableViewer/tableView.aspx
  5. Statistics SA – 2011 Census information http://www.statssa.gov.za/publications/P0302/P03022011.pdf
  6. SABS Building Code SANS 10400-A:2010 https://www.sabs.co.za/content/uploads/files/SANS10400(colour_and_looseleaf).pdf
  7. Statistics SA Community Survey 2007 http://www.statssa.gov.za/community_new/content.asp