Journal of Coastal Conservation 2: 63-72, 1996 © EUCC; Opulus Press Uppsala. Printed in Sweden
The degradation of plastic litter in rivers: implications for beaches
& Simmons, S.L.2
1School of Applied Sciences, University of Glamorgan, Pontypridd, Taff-Cynon-Rhondda, Wales, UK; 2Dewplan Ltd, Beechwood Hall, Kingsmead Road, High Wycombe, Bucks, UK; *Tel. +44 1443 482280; Fax +44 1443 482285
Abstract. Polythene sheeting is a major litter component on estuarine beaches and river banks. Sanitary towel backing strips, which are one of the commonest items of sewage related debris found on beaches, enter the riverine system via combined sewer overflows. Investigations on these items, positioned at natural riverine stranding levels, showed that after an initial rapid breakdown little further loss of tensile strength occurred. Experiments carried out on backing strips, buried in the bank, suspended from a tree and tethered to the bank, showed significant change. Buried samples retained the greatest tensile strength retention, dropping no lower than 90 %, the other samples showed similar retention rates at 80 %. The difference is probably due to photodegradation as biodeg- radation effects were minimal. Probably, the longevity of such plastics is a major reason for their abundance and widespread distribution both on river banks and beaches.
Keywords: Biodegradation; Photodegradation; Sanitary towel; Tensile strength.
Coastal conservation bodies such as Friends of the Earth, frequently spend days picking up beach litter (Anon. 1992a) and Councils spend large sums of money in beach litter cleanups. For instance, Kent County Council, UK, spend some $15 million to clean their beaches (Gilbert pers. comm.), and another $150 000 is required to clean up the beach in summer at Weston Super Mare, UK. This encourages volunteers but is often a waste of time as within days an equivalent amount of litter will have returned (Simmons & Williams 1993). Plastic litter is very common on many beaches, as has been described in numerous publications (e.g. Scott 1972; Lentz 1987; Pruter 1987, Laist 1987; Anon. 1992a-c; Nash 1992; Simmons et al. 1993; Simmons & Williams 1993, 1994). The present paper describes plas- tics, derived in the main from fly tipping sites or com- bined sewer overflows that enter the river system and end up on a beach. Marine litter research is some 25 years old; research on riverine litter is in its infancy, yet some 80 % of the litter on the estuarine beaches of South
Wales, UK, comes from this source (Anon. 1992b, c; Williams et al. 1993a, b; Simmons & Williams, 1994; Williams & Simmons 1995). Any region with large rivers entering the sea will input large amounts of litter into the coastal system from source but quantification remains to be resolved. One particular aspect of riverine litter which appears to cause great aesthetic offence, resulting in many public complaints, is the stranding of plastics along the length of rivers (Anon. 1991; Anon. 1992d). This study quantifies plastic degradation in the river Taff in South Wales, UK. which enters the sea at Cardiff. The ‘flashy’ nature of rivers in South Wales and resultant flow fluctuations, allow litter items to be trans- ported considerable distances until they are filtered by suitable obstructions, often vegetation. Physical charac- teristics of some litter items allow them to become entangled in the vegetation and be stranded when the water level recedes resulting in a ‘Christmas tree’ adorn- ment. This is more conspicuous when water levels have fallen and during winter months when lack of foliage offers less camouflage (Fig. 1). The materials move down stream in an episodic fashion and accumulate at the beach area.
One particular polyethylene product commonly found along river banks and beaches, the sanitary towel back- ing strip, was deemed appropriate for investigation. Not only does this product contribute to the overall aesthetic nuisance of litter, but also impinges upon broader issues such as health and safety. The sanitary towel market is expanding and by 1990 the sanitary protection split between towels and tampons was 56 % to 44 % (Anon. 1990a; Howarth pers. comm.). With the recent introduc- tion of daily use panty-liners, contributing 28 % of the market (Howarth pers. comm.), towels obviously con- stitute a waste disposal problem. Smith and Nephew Products Ltd. estimated that 72 % of all towels are flushed (Howarth pers. comm.) and with the still largely archaic and ineffective screening in UK sewerage sys- tems, their contribution to riverine plastic as a whole could be fairly substantial. In light of these facts, panty- liner backing strip degradation trials were initiated.